DEC CFBC Boiler Manual

PROJECT

8 X 135 MW LIGNITE THERMAL POWER PLANT BHADARESH, DISTT. BARMER, RAJASTHAN - INDIA

OWNER

RAJ WEST POWER LIMITED (RWPL) RAJASTHAN - INDIA

ENGINEERS

DESEIN PRIVATE LIMITED NEW DELHI INDIA

BTG SUPPLIER

DONGFANG ELECTRIC CORPORATION CHENGDU CHINA

ORIGINATOR MANUFACTURER

DONGFANG BOILER GROUP CO., LTD. ZIGONG CHINA

Document No.: 39J SM Rev.: A

Document Title :

OPERATION INSTRUCTION FOR CFB BOILER

Doc.No.: 39J-SM Operation Instruction for CFB Boiler Page 2 of 104 Rev. A

Document No. 39J-SM

OPERATION INSTRUCTION FOR

CIRCULATING FLUIDIZED BED BOILER ( CFBB )

PREP.

CHKD.

EXAM.

APPD.

AUTD.


REVISION RECORD

PAGE REV. REVISIONS REVISED REV. DATE. REV.SHEET

No.

All A First Issue


PREFACE The Circulating Fluidized Bed (CFB) Boiler, whose model is DG440/13.73-II14, is specially designed and manufactured by DONGFANG BOILER GROUP CO., LTD. (DBC) for INDAI RAJ WEST POWER LIMITED POWER PLANT. The boiler is a superhigh pressure 135MWe CFB boiler. This operation instruction is issued to assist operators of DBCs equipment in obtaining the best operation results. This operation instruction is to be used as a guide for operational reference and shall not take the place of Boiler Operation Specifications. This operation instruction can only supplement the experience and judgments of personnel in charge of operation. It shall be interpreted and applied after giving careful consideration of the requirements of other relative equipment and for any particular set of circumstances. This operation instruction does not purport to cover all details or variations of equipment, including every contingency to meet during operation and / or maintenance. The recommendations contained in the operation instruction are prepared by DBC based upon the knowledge and experience gained in the manufacture of CFB boilers, and they represent our best experience and judgments at present. However, in the application of this operation instruction to pre-operation, operation and maintenance of equipment, DBC assumes no responsibility for any failure or incident resulted from incorrect operation. As the successful operation and performance depend greatly upon auxiliary systems, this operation instruction contains some brief descriptions for several vital systems such as coal feed system, air and gas system, bed material extraction system, limestone feed system, etc. They shall be understood as the fundamental requirements of the Boiler and could not be regarded as the sole principles for power plant design. Without permission, no one that is not involved in this Project is allowed to make any copy of this operation instruction.


TABLE OF CONTENTS

DONGFANG BOILER GROUP CO., LTD. ....................................................................................................1 SECTION 1 CONSTRUCTION DESCRIPTION ............................................................................8 1.1 Design Conditions......................................................................................................................................8 1.1.1 Boiler Specifications..............................................................................................................................8 1.1.2 Boiler Main Dimensions........................................................................................................................9 1.1.3 Fuel..........................................................................................................................................................9 1.1.4 Ash Characteristics .............................................................................................................................10 1.1.5 Limestone for Desulfurization ...............................................................................................................11 1.1.6 Igniter Type ,Fuel for Ignition and Combustion Support................................................................12 1.1.7 Feedwater Quality ...............................................................................................................................13 1.1.8 Fountain ................................................................................................................................................13 1.1.9 Natural Conditions............................................................................................................................13 1.1.10 Operation Mode.................................................................................................................................14 1.1.11 Draft Mode..........................................................................................................................................15 1.2 General Description Of DONGFANG Type CFB Boiler ..........................................................................15 1.2.1 CFB Technology Description................................................................................................................15 1.2.2 DONGFANG Type CFB Boiler Process...........................................................................................17 1.3 General Description of DG440/13.73-II14 ...................................................................................................19 1.3.1 General Arrangement OF DG440/13.73-II14 Type CFBB ............................................................19 1.3.2 Boiler Steam and Water Flow Path ..................................................................................................22 1.3.3 Boiler Gas and Air Flow Paths .............................................................................................................25 1.3.4 Combustion and Circulation Process of the Materials......................................................................26 1.3.5 Fuel and Limestone Feed Systems and Ash Removal System ......................................................28 1.3.6 Expansion System .................................................................................................................................28 1.3.7 Sootblowing System ...........................................................................................................................29 1.4 Main Equipment of CFB Boiler....................................................................................................................30 1.4.1 Economizer ..........................................................................................................................................30 1.4.2 Steam Drum and Drum Internals ......................................................................................................30 1.4.3 Furnace .................................................................................................................................................30 1.4.4 Cyclone .................................................................................................................................................31 1.4.5 The Rear Pass .....................................................................................................................................32 1.4.6 LTS ........................................................................................................................................................32 1.4.7 Primary Desuperheater ......................................................................................................................32 1.4.8 PSH .......................................................................................................................................................33 1.4.9 Secondary Desuperheater .................................................................................................................33 1.4.10 HTS ........................................................................................................................................................33 1.4.11 Reheater Emergence Desuperheater ...............................................................................................34 1.4.12 LTR.........................................................................................................................................................34 1.4.13 Reheater Micro Spray Desuperheater ..............................................................................................34 1.4.14 PRH........................................................................................................................................................34 1.4.15 Air Heater ..............................................................................................................................................35 1.4.16 U Valve ..................................................................................................................................................35 1.4.17 Ash Cooler..........................................................................................................................................36 1.4.18 Ignition System ..................................................................................................................................36


1.4.19 Abrasion proof and refractory materials ........................................................................................37 1.4.20 Boiler Steel Structure........................................................................................................................38 1.5 Water Volumes Of Major Boiler Parts: .....................................................................................................38 SECTION 2 SAFETY PRECAUTIONS AND PREPARATION FOR OPERATION.........................40 2.1 SAFETY PRECAUTIONS......................................................................................................................40 2.2 HYDROSTATIC TESTS...........................................................................................................................43 2.3 SOLIDIFYING REFRACTORY MATERIALS .......................................................................................47 2.4 BOILING OUT........................................................................................................................................47 2.4.1 General .................................................................................................................................................47 2.4.2 Recommended Chemicals for Boiling Out.......................................................................................48 2.4.3 Preparations for Boiling Out...............................................................................................................49 2.4.4 Boiling Out Procedure.........................................................................................................................52 2.5 FEEDWATER AND BOILER WATER TREATMENT ..........................................................................54 2.6 CHEMICAL CLEANING OF ECONOMIZER AND STEAM GENERATING CIRCUIT.....................55 2.6.1 General .................................................................................................................................................55 2.6.2 Determining the Need for Chemical Cleaning.................................................................................55 2.6.3 Solvent System ....................................................................................................................................56 2.6.4 General Cleaning Operations ............................................................................................................57 2.7 CHEMICAL CLEANING OF SUPERHEATERS & REHEATERS........................................................58 2.8 BOILER SYSTEM AIR TEST..................................................................................................................58 SECTION 3 OPERATION AND MAINTENANCE .........................................................................60 3.1 GENERAL.................................................................................................................................................60 3.2 IMPORTANT PRECAUTIONS..............................................................................................................60 3.2.1 Furnace doors ....................................................................................................................................60 3.2.2 Furnace Pressure Limits ..................................................................................................................61 3.2.3 Drum Water Level and Temperature Difference...........................................................................62 3.2.4 Safety Valve Adjustment ..................................................................................................................63 3.2.5 Excess Air Requirements .................................................................................................................63 3.2.6 Bed Temperature Profile ..................................................................................................................64 3.2.7 Others..................................................................................................................................................65 3.3 COLD STARTUP PROCEDURE ...........................................................................................................67 3.3.1 Preparation Prior to Startup .............................................................................................................67 3.3.2 Purging................................................................................................................................................71 3.3.3 Warming the Unit...............................................................................................................................77 3.3.4 Start-up (Fuel Firing).........................................................................................................................81 3.4 HOT RESTART ........................................................................................................................................85 3.5 NORMAL OPERATION.........................................................................................................................88 3.5.1 Combustion ..........................................................................................................................................88 3.5.2 Boiler feedwater and steam quality ..................................................................................................90 3.5.3 Sootblowing..........................................................................................................................................90 3.5.4 Spray Attemperation ...........................................................................................................................91 3.5.5 Reheated Steam Temperature Regulation......................................................................................91 3.6 NORMAL SHUTDOWN ........................................................................................................................92 3.7 EMERGENCIES......................................................................................................................................95 3.7.1 Main Fuel Trip (MFT) ..........................................................................................................................95 3.7.2 Emergency Operating Procedure ...................................................................................................96


3.7.3 Overpressure Protection ....................................................................................................................99 3.8 MAINTENANCE ......................................................................................................................................99 SECTION 4 ATTACHMENT........................................................................................................103 4.1 Boiler Performance data summary sheet(I) Performance coal 100%B-MCR condition.....................103


SECTION 1 CONSTRUCTION DESCRIPTION

1.1 Design Conditions

1.1.1 Boiler Specifications

Boiler capacity: under such conditions as firing performance coal or check coal

stated in item 1.1.3 and limestone stated in item 1.1.4 with the size distribution

specified in fig. 1.1~1.2, design Ca/S molar ratio, rated feed water temperature, rated

main steam temperature, rated pressure and acceptable steam quality, the boiler

maximum continuous rating is 440 t/h at least.

The boiler maximum continuous rating (BMCR) is corresponding to turbine regulating

valve whole open (VWO) condition.

Pressure, temperature and flow of main superheated steam, reheated steam and

feeder water of the CFBB can match with turbine parameters.

Boiler Type: DG440/13.73-II14

BMCR

Maximum Steam Flow 440t/h

Superheat Steam Outlet Pressure 13.73MPa(g)

Superheat Steam Outlet Temperature 540 Reheat Steam Outlet Temperature 540 Reheat Steam Outlet Pressure 2.57MPa(g)

Reheat Steam inlet Temperature 320 Reheat Steam inlet Pressure 2.73MPa(g)

Reheat Steam Flow 356.114t/h

Feedwater Temperature 248.6 Notes: Above mentioned (g) indicates gauge pressure.


1.1.2 Boiler Main Dimensions

Furnace Width (Between CL of Side Walls) 17170mm

Furnace Depth (Between CL of Front & Rear Walls) 7492mm

Elevation of Steam Drum CL 48370mm

Elevation of Boiler Top 54500mm

Boiler Width 31400mm

Boiler Depth 37100mm

1.1.3 Fuel

Performance coal in this project is asphaltite, a local reserve in the region. The coal

analysis data are as follows:

Item Symbol Unit Performance Coal Worst Coal

Sulfur as received Sar % 1.2 0.5

Hydrogen as received Har % 2.5 1.4

Carbon as received Car % 30 22.2

Nitrogen as received Nar % 0.3 0.3

Oxygen as received Oar % 9.3 7.6

Ash as received Aar % 11.7 30

Total Moisture Mt % 45 38 Volatile matter as dry and ash free Vdaf % 25 20

HHV as received Q Cal/kg 2900 2001 Coal Size Distributiondmax=12mmd50=1.8mm. (See Fig. 1.1Coal Size

Distribution Curve).

Notes: To achieve optimum conditions for the CFB combustion process, the

solid fuel has to be prepared with respect to maximum particle size and

grain size distribution. The recommended coal size distribution is based on

both the balance of solid and emission, which can achieve optimum

combustion and a reasonable emission. Solid fluidizing velocity selection is

based on coal size, and fluidizing velocity defines furnace section. So the


coal size is a most important parameter. If the inlet coal size is too large, it

will affect stable operation of the ash-cooler and lead to higher carbon

content in bottom ash; on the contrary, it will lead to higher carbon content

in fly ash.

Fig. 1.1 Coal Size Distribution Curve

1.1.4 Ash Characteristics

Compositions of ash (with no limestone sophisticated)

Composition Symbol Unit Performance Coal Silicon dioxide SiO2 % 5070 Aluminum trioxide Al2O3 % 1030 Ferric trioxide Fe2O3 % 26 Titanium oxide TiO2 % 12.5 Calcium oxide CaO % 0.5610 Kalium oxide K2O % 0.050.3 Sodium oxide Na2O % 014.2 Magnesia MgO % 0.414.83


Sulfur trioxide SO3 % 010 Chlorid Cl % 0.010.25

1.1.5 Limestone for Desulfurization

Limestone is used in this project for desulfurization. Limestone analysis data are as

follows:

Composition Symbol Unit Value Loss of combustion L.O.I 42.443.2 Calcium Carbonate CaCO3 9597 Sodium Carbonate MgCO3 0.30.75 Silicon dioxide SiO2 0.81.4 Aluminum trioxide Al2O3 0.40.6 Ferric trioxide Fe2O3 0.10.24 Calcium oxide CaO 53.9554.6 Magnesia MgO 0.20.6 Limestone Size Distributiondmax=1.5mmD50=0.45mm. (See Fig. 1.2

Limestone Size Distribution Curve).

Notes: After limestone powder is injected into the furnace, it is reacted with

SO2 and removes SO2, to guarantee the effective and economical operation

of boiler. The proper limestone size distribution is very important. If the

limestone particle is too coarse or too fine, it will affect the circulation

procedure. The too coarse particle will lead to increased limestone

consumption and will make bed temperature lower than normal value and

bottom ash quantity higher than design value; and the too fine limestone

particle will lead to its inadequate residence time in main circulating loop to

make limestone consumption increase and fly ash quantity higher than

design value.


Fig. 1.2 Limestone Size Distribution Curve

1.1.6 Igniter Type ,Fuel for Ignition and Combustion Support

The boiler is equipped with four (4) in-duct diesel oil burners , six (6) over-bed heavy

oil burners which are located at the side waterwall, The over-bed heavy oil burners

can be only used to support the combustion at low load.

The in-duct burners firing diesel oil are only used for the low load combustion

support.

The diesel oil analysis data are as follows:

Item Unit Value

Kinematic viscosity(40) cSt 2.5 to 15.7

Density (15) (approximation kg/m3 850 - 870

Flash piont (min) o C 66

Pour point (max) o C 12(winter21 (summer)

Water(max) % vol. 0.25

Sediment and Water (max) % wt 0.10

Sulphur (max) % wt 1.8


Item Unit Value

Ash (max) % wt 0.02

HHVapproximation Kcal/kg 10,000

1.1.7 Feedwater Quality

Make-up water: one stage desalination and blend bed.

Boiler normal continuous blowdown rating: 0.3-1%

Boiler water and steam quality shall be in compliance with the requirements of

superhigh pressure boiler in the Quality criterion of Water and Steam for

generating unit and Steam power equipment (GB/T12145-1999).

Item Feedwater

PH value 8.8~9.3

Full salinity /

hardness 2.0mol/L

Hydrazine (N2H4) 10-50g/L (Volatility treatment)

Dissolved oxygen (O2) 7g/L

Fe 20g/L

Cu 5g/L

Oil 0.3mg/L

1.1.8 Fountain

The fountain of this power plant is from IGNP River .

1.1.9 Natural Conditions

Power plant address Bothya city of Rajasthan, Indian height above sea level 184m Maximum daily average temperature in May 40


Minimum daily average temperature in December 12

Maximum daily temperature 34.5 Minimum daily temperature 20.7 Recoding Maximum temperature 48.9 Recoding Minimum temperature -1.7 Humidity 2379 Maximum precipitation from July to September 263mm

Annual wind speed 8.5kmm/h Maximum wind speed 24km/h Basic wind speed 47 m/s Modulus K1 1.07 Seismic zone in India 1 Modulus K3 According to IS:875

1.1.10 Operation Mode

1) Load characteristic: The boiler will operated under normal load and can regulate

peak load. The boiler can meet double shift operation requirements.

2) Coal feeding system: Two-stage crushing plus screen system is adopted in this

project to satisfy requirements of coal size distribution.

3) Feed water regulating: Two (2) 100% BMCR motor-driven feed water pumps.

4) Bypass system: Two in-series stage bypass system with capacity of 60%BMCR.

5) Bottom ash removal: Bottom ash is discharged continuously or periodically

through ash cooler.

6) Air heater shall not be arranged in the inlet duct of air preheater.

7) The available average operating hours are more than 7500h per year.

8) Compressed air pressure: 0.5~0.7MPa; electric voltage: AC 400V/230V; DC 220V;


motor protection degree: IP54.

1.1.11 Draft Mode

Balanced draft is adopted for this boiler. The balance point of draft system is set at

the top of furnace (cyclone inlet).

1.2 General Description Of DONGFANG Type CFB Boiler

1.2.1 CFB Technology Description

As a cleaning coal combustion technology, the Circulating Fluidized Bed (CFB)

technology has been successfully used in boilers all over the world since 1980s.

The various types of solid fuel combustion systems historically available, such as

stokers, pulverized fuel, and cyclone-fired boilers have distinct and specific

advantages and disadvantages. A few of the disadvantages that are common to each

of them in varying degrees are: Low residence time of fuel in the combustion zone

(except stokers) requires high combustion temperatures to assure adequate

combustion efficiency without excessive unburned carbon losses. High temperatures,

usually more than 980C, contribute to the formation of nitrogen oxides, which are

environmentally objectionable. High combustion temperatures also dictate the use of

post-combustion treatment scrubbers for removal of sulfur dioxide (SO2). When the

combustion temperature is maintained between 850C and 900C, SO2 removal can

be accomplished by injecting limestone (CaCO3) directly into the furnace. The low

ash fusion temperature of many solid fuels goes against the adoption of conventional

combustion systems because the higher combustion temperatures result in the

formation of slag on boiler heat transfer surfaces. The need to overcome these

difficulties when using low-grade fuels has led to the development of fluidized bed

combustion systems. Presently, there are two distinct types of fluidized bed boilers in

commercial operation: bubbling bed and circulating bed.


1.2.1.1 Bubbling Bed

In the bubbling bed-type boiler, a layer of solid particles (mostly limestone, sand, ash

and calcium sulfate) are concentrated on a grid near the bottom of the boiler. This

layer is maintained in a turbulent state as low velocity air is forced into the bed from a

plenum chamber beneath the grid. Fuel is added to this bed and combustion takes

place. The combustion air velocity of is kept at a minimum value, but it is quite

enough to maintain turbulence in the bed. This velocity is not high enough to carry

significant quantities of solid particles out of the furnace. This turbulent mixing of air

and fuel results in a residence time of five seconds. The combination of turbulent

mixing and residence time permits bubbling bed boilers to operate at a furnace

temperature below 890C. At this temperature, limestone is mixed with fuel in the

furnace to achieve over 90% sulfur removal. Boiler efficiency is the percentage of

total energy in the fuel that is used to produce steam. Combustion efficiency is the

percentage of complete combustion of carbon in the fuel. Incomplete combustion

results in the formation of carbon monoxide (CO) in the flue gas plus unburned

carbon in the solid particles leaving the furnace. In a regular bubbling bed boiler,

combustion efficiency can be up to 92%, with its unburned carbon loss component of

kept within the range of 2% to 5%. This is a good figure, but it is lower than that

achieved by pulverized fuel or cyclone-fired boilers. In addition, some fuels that have

very low volatile matter cannot be completely burned within the solids residence time

in bubbling bed-type boilers.

1.2.1.2 Circulating Fluidized Bed (CFB)

The need to improve the fluidized bed combustion efficiency (which also increases

overall boiler efficiency and reduces operating costs) and the desire to burn a wider

range of fuels has led to the development and application of the circulating fluidized

bed (CFB) boiler. Through the years, boiler suppliers have been increasing the size

of these high-efficiency steam generators. The CFB process offers the means for

efficiently burning a wide variety of fuels while maintaining low emissions. Fuel is fed

to the lower furnace where it is burned in an upward flow of combustion air. Fuel, ash,


and unburned fuel carried out of the furnace are collected by a separator and

returned to the lower furnace. Limestone, which is used as sulfur sorbent, is also fed

to the lower furnace. Furnace temperature is maintained in the range of 850C to

950C by suitable heat absorbing surface. This process offers the following

advantages:

Fuel Flexibility The relatively low furnace temperatures are less than the ash

softening temperature for nearly all fuels. As a result, the furnace design is

independent of ash characteristics, which allows a given furnace to handle a wide

range of fuels.

Low SO2 Emissions Limestone is effective sulfur sorbent in the temperature range

of 850C to 950C. SO2 removal efficiency of 95% or even higher has been

demonstrated along with good sorbent utilization.

Low NOx Emissions Low furnace temperatures (850C to 950C) plus staging of air

feed to the furnace produces very low NOx emissions.

High Combustion Efficiency The long solids residence time in the furnace resulting

from the collection/recirculation of solids via the cyclone, plus the vigorous solids/gas

contact in the furnace caused by the fluidization airflow, results in high combustion

efficiency, even with difficult-to-burn fuels. The unburned carbon loss component of

the combustion efficiency is typically in the range of 1% to 2%.

1.2.2 DONGFANG Type CFB Boiler Process

The major components of a DONGFANG CFB boiler are :

z The solids circulation loop, comprising the furnace, the cyclones, U valves.

z The rear pass.

In the CFB process, combustion and desulphurization take place within a large mass

of highly agitated fine ash particles bed at a relatively low temperature (close to 850

900C) depending upon the fuel reactivity. This temperature is chosen to facilitate the

increase of combustion rate and desulphurization efficiency for the coal considered.


The bed temperature of this boiler is 897.

These particles or "solids" are held in suspension (fluidized) section by an upward

flow of air blown into the bottom of the furnace as the primary air through the

fluidization nozzles. The secondary air is fed into the furnace at two levels, thus

realizing staged combustion.

The bed completely fills the furnace volume (its density, high in the lower part, rapidly

decreases with height). The separation of solids from the gas solids stream at the top

of the furnace is ensured by means of cyclones.

The balance of solids is ensured by directly recirculating the solids separated from

the gas solids stream to the lower part of the furnace through material recycle

equipment (U valve). These U valves are installed to ensure that any gas flows

directly from the furnace to the cyclones.

The fluidization regime in CFB loop is characterized by very strong agitation and

mixing, high solids internal and external recirculation, high gas/solids slip velocity

and long residence time due to the high efficiency of cyclones.

All these result in excellent conditions regarding heat transfer and chemical

reactions.

The flexibility induced by the process allows burning a wide range of fuels

("opportunity fuels"), with a single design adopted.

Regarding depollution, the CFB boiler has very good performance due to the

following reasons:

The CFB boiler is able to remove sulfur dioxide directly in the furnace. This is

accomplished by contact between sulfur oxide and the calcium oxide contained in the

coal ashes or in the added limestone. The limestone is calcined in the furnace to

form calcium oxide (CaO) and then reacts with the SO2 to form calcium sulfate,

shown as follows:

CaCO3 CaO + CO2


CaO + SO2 + O2 CaSO4

This reaction takes place preferably at 850-900C, which can be kept under a wide

range of operating loads.

Further, the staged combustion and the relatively low combustion temperature

reduce NOx formation to a large extent.

So, CFB process offers:

z an intense internal mixing of the particles (fuel, limestone, hot ashes constituting the bed)

z a homogeneous temperature in the bed

z a long residence time of the fuel in the furnace

z the possibility to keep the temperature within the optimum range of SO2 capture by the limestone

The combination of these characteristics offers the following advantages in terms of

performance:

z high carbon burnout

z high desulphurization efficiency

z low NOx emission

z high flexibility of operation.

1.3 General Description of DG440/13.73-II14

1.3.1 General Arrangement OF DG440/13.73-II14 Type CFBB

DG440/13.73-II14 CFB boiler adopts single drum, natural circulation, circulating

fluidized bed combustion and full enclosure structure, which is mainly composed by

membrane waterwall furnace, two plate cyclones and the rear pass.

The boiler adopts membrane wall furnace. Inside the furnace, eight platen


superheaters, four platen reheaters and one split waterwall are arranged. Six coal

feeders and four limestone feeding inlets are arranged on the lower front waterwall.

The bottom of the furnace is a water-cooled air plenum enclosed by the waterwall

tubes, connecting with the primary air ducts which are at each side of the boiler.

There are two induct burners in each PA duct. The burners are equipped with high

energy ignitor. And six over-bed burners are arranged above the grid for low load

combustion support. In the rear of the furnace, two rolling ash-coolers are arranged.

Between the furnace and the rear pass, two plate cyclones lined with refractory are

arranged. At the bottom of each cyclone, a non-mechanical U-valve seal device is

installed. The dual-element convection rear pass (double flue) is adopted for the

steam-cooled rear pass in the RH and SH area. The cold reheater is arranged in the

front flue and the hot superheater & cold superheater are arranged in the rear flue.

After that the two gas streams will become one stream and pass through economizer.

Then gas is divided into two streams to go through tubular air heater. The air heater

is of double in-let and out-let arrangement along the boiler width direction. Two stage

spray water will be adopted to the superheater system and damper regulation is

adopted to the reheater system. And emergency and micro spray water

desuperheaters are adopted for the safety guarantee of the reheater system.

The boiler is symmetrically arranged from right to left and is suspended or supported

from the boiler steel structure. The steel structure consists of columns, beams and

bracings.


Fig. 1.3 Side view of Boiler


Fig. 1.4 Plan View of Boiler

1.3.2 Boiler Steam and Water Flow Path

Single unit system is adopted in main steam, reheater steam and feeder water

system. And double in-let-and-out-let connection is adopted in main steam and

reheater steam pipe arrangement.

Feedwater is sent to the two sides of economizer inlet header in the rear pass. It

flows upstream and passes the horizontally arranged economizer tubes. Collected in

the outlet header of economizer, it is routed by the connecting pipe into the drum

from the drum head. In the period of boiler start-up, no continuous feedwater flows

into the drum. Economizer recirculation system can direct boiler water from the drum

to the inlet header of economizer, preventing water from steaming in the economizer


tubes.

Fig. 1.5 Steam and Water Flow

The DG440/13.73-II14 CFB boiler is of natural circulation. Boiler water circulation

system adopts centralized downcomers and decentralized feeders and risers. Water

from Economizer is directed into the water space of drum, then it enters into the

waterwall inlet header by the downcomers and feeders. Water is heated to the

mixture of steam/water and flows upward through the furnace waterwall and split

waterwall. Out of the waterwall outlet header, the mixture of steam/water is routed by

risers into the drum for steam/water separation. The split waterwall forms an

independent circuit with the separate feeder and riser for the safety and reliability of

water circulation. The separated water reenters the water space in the drum and

circulates again. The separated saturated steam is directed out from the steam

connecting pipe on the top of the drum.

Coming out of the drum, the saturated steam is directed to the upper header of the

side wall of the rear pass area by the connecting pipe. Then it passes the front, rear

walls and middle wall of the rear pass area and joins in the inlet header of low


temperature superheater (LTS). After flowing through the tubes of LTS, it is directly

induced into the platen superheater (PSH) in the upper furnace by the connecting

pipe. Passing the PSH, it returns to the high temperature superheater (HTS) in the

rear pass. At last, the steam with the rated pressure and temperature is directed out

from two ends of the outlet header of hot superheater.

The superheater system adopts spray desuperheating as a method for temperature

control and protection of heating surface tubes. The whole superheater system is

arranged with two stages of spray attemperation. The primary desuperheaters (on

the connection pipes of each side of the boiler) are arranged on the connecting pipe

from the LTS to the PSH for coarse adjustment. The secondary desuperheaters (also

on the connection pipes of each side of the boiler) are located on the connecting pipe

from the PSH to the HTS for fine adjustment. In the two stages of spray

attemperation, the quantity of spray water on each side can be adjusted

independently to eliminate the steam temperature difference on the right and left

sides.

The cold reheated steam coming from HP of turbine is induced into the low

temperature reheater (LTR) located in the front flue in the rear pass. After flowing

upward through two banks, it is directly induced into the platen reheaters (PRH) in

the upper furnace by connecting pipe. Heated by the PRH, the reheated steam with

the rated pressure and temperature is induced into MP of turbine.

The reheated steam temperature can be adjusted through regulating gas damper

located at the back of the double flue to adjust gas flow through RH flue. Its a main

method to regulate RH temperature. The RH spray system is also used for faster

adjustment and the safety guarantee of the RH system. The whole reheater system

is arranged with two stages of spray attemperation. The primary desuperheaters (on

the connection pipes of each side of the boiler) are arranged on the inlet connecting

pipe of the LTR for emergence condition. The secondary desuperheaters (also on the

connection pipes of each side of the boiler) are located on the connecting pipe from

LTR to the PRH for faster and more precise adjustment. In the two stages of spray

attemperation, the quantity of sprayed water on each side can be adjusted


independently to eliminate the reheater steam temperature difference.

1.3.3 Boiler Gas and Air Flow Paths

Material circulation in the CFB boiler is started and maintained by forced-draft fans

(including primary and secondary air fans) and induced-draft fans.

Air from the primary air fan is sent into the furnace though three paths:

The first path: Hot air after the primary air heater enters into the water-cooled air

plenum at the bottom of furnace. The air coming out of nozzles on the air distributor

fluidizes bed materials. Gas and solid-phase flow is formed, which goes upward

through the furnace.

The second path: Hot air after the primary air heater is pressurized by the blower and

is directed as coal-distributing medium to the air-swept coal spouts.

The third path: Cold air induced before the primary air heater is used as the sealing

air for the belt coal feeders.

Air from the secondary air fan is sent to the furnace from the two layers of overfire

airports on the front and rear walls after the secondary air heater.

Gas and entrained solid particles exit the furnace from the outlet on the upper rear

waterwall and enter into the cyclone from the cyclone inlet flue. In the cyclone, most

of the solid particles are separated from the gas. Cleaned gas is induced out from the

discharge pipe (inner barrel) of the cyclone and directed to the rear pass by the

cyclone outlet flue. It flows into the rear pass from the inlet on the front wall and

sweeps across the LTR, HTS, LTS, economizer and air heater, transferring heat to

the heating surfaces. Then, the gas is routed through the dust collector and finally

sent into the stack by the induced-draft fan and emitted into the atmosphere.

The U-valve seal device is equipped with three blowers with high-pressure head. The

output of each blower is 50% of the total air needed of the U -valve seal device. In

normal operation, two blowers are in service and one blower is standby. The blowers

are of constant volume type. The air flow is adjusted through bypass pipe to the


primary air path.

The boiler is of balanced-draft type. The balance pressure point is located at the top

of the furnace.

Full enclosure structure is adopted to this boiler. The operation floor elevation is

9.0m.

Fig. 1.6 Diagram of Air and Gas Flow, Fuel, Limestone, Ash systems

1.3.4 Combustion and Circulation Process of the Materials

The cold start-up procedure of boiler is as follows:

Feed the start-up materials to the bed and U valves;

Start the in-duct burner and send the heated combustion air with the temperature of

870 to the furnace through the water -cooled air distributor for heating the start-up materials.

As the bed temperature reaches 540 and remains stable, the crushed 0 12mm coal particles are sent into the dense-phase zone of the furnace from the six coal

feeders and the crushed limestone particles for desulphurization are sent into the

furnace from the limestone feeding inlets.


Under the rated load condition, the primary air (about 40% of the total combustion air)

passes through the water-cooled air plenum and enters into the furnace as

combustion air and fluidizing medium of materials in the bed. The secondary air is

directed into the furnace from the two layers of overfire airports on the front and rear

walls to guarantee enough combustion air for coal particles and participate in the

adjustment of combustion. At the same time, the staged secondary air can produce

local reducing atmosphere in the furnace and inhibit oxidation of nitrogen in the fuel

so as to decrease generation of NOx.

At the bed temperature of 864 , air fully mixes with fuel and limestone in the dense-phase zone at the lower furnace. Firing of coal particles releases a part of

heat. CaCO3 is calcined to produce CO2 and CaO; the unburned coal particles are

entrained by gas in the diluted-phase zone at the upper furnace for further

combustion. The upper furnace is also a main desulphurizing zone, where CaO and

SO2 produced by combustion react to produce CaSO4.

The gas entraining rich solids passes through the furnace from two gas outlets on the

upper rear water wall. Then, it enters into two plate cyclones for the solids and gas

separation.

After leaving the plate cyclones and vortex finders, separated hot flue gas passes

through the refractory lined cross-over duct and enters into the top of the dual-flue

rear pass of the boiler. The flue gas splits and flows into the superheating section and

the reheat steaming section. The gas flow distribution of the two sections is decided

by dampers at the outlet of each section. As flue gas flows downward in this steam

cooled section, heat is transferred from the hot flue gas into the reheat steam and

superheat steam. The economizer is located directly below these steam sections. Air

heaters are located in the back of the rear pass. The horizontal tubular air heaters

are devices that heat primary/secondary air before it enters the boiler. Air is heated

as it passes inside the tubes, and the hot flue gas gives up its heat as it flows outside

the tubes. At the outlet of the boiler, gas temperature has decreased to about 149 . The separated solids by the cyclone are reinjected by means of the non-mechanical

U-valve seal device back to the furnace for circulating combustion.


On the rear wall of the lower furnace, two bed material drain ports are arranged. By

controlling the flow of ash extraction, the bed and furnace pressure profiles are kept

within the design limits to guarantee the good operation of boiler.

1.3.5 Fuel and Limestone Feed Systems and Ash Removal System

Six (6) coal feeders and four (4) limestone feed points are located at furnace front

wall. Four (4) bed material feed points for start-up are located in U-valve, which are

used to feed bed material when boiler start-up or to add bed material during

operation if necessary.

The bed ash from furnace is drained down to two (2) rolling ash coolers. A bed ash

removal system is connected to the rolling slag cooler ash outlet, the rear pass ash

drain (below air heater) and the ESP ash drain.

1.3.6 Expansion System

The expansion centers (fixed points) are designed according to the features of boiler

arrangement and supporting structure. This boiler has seven zero expansion points,

such as:

z The center line of furnace rear wall

z The center line of cyclone support (two points)

z The center line of u valve support (two points)

z The center line of rear pass front wall

z The center line of air heater support.

Each expansion system is expanded outwards from its fixed points through the

limitation and guide equipment. At the same time, the guide equipment of thermal

expansion will transfer wind and seism load to the steel structure.

The furnace waterwall and the rear enclosure wall expand downwards as they are all

hung onto the top plates. The furnace expands from the furnace center line (fixed


point) toward two sides through the expansion control devices. The rear pass heating

surfaces expands from boiler center line (fixed point) toward two sides through the

expansion control devices also. Material recycle equipment, cyclone and air heater

expand upwards from their supporting bases, and symmetrically expand onwards

and backwards, leftwards and rightwards.

There is a large temperature difference between furnace, Cyclone and U valve. And

the expansion ratios of the materials for these parts are not the same. So Cyclone

and U valve are supported on the corresponding steel structures respectively. Due to

their large expansion differences and huge dimensions, non-metal expansion joint is

adopted between furnace and cyclone. Metal expansion joints are adopted between

U valve orifice and furnace and between cyclone cone section outlet and U valve to

absorb expansion difference.

The expansion indicators shall be located inside the boiler proper.

1.3.7 Sootblowing System

A complete set of automatic sootblowing equipment is provided to clean the

superheater, reheater and economizer installed in the rear pass and the air heater

elements during operation of the boiler.

Steam for the sootblowers is taken from the outlet header of the low temperature

superheater. The tube socket specification is 606. The steam parameter for sootblower is 14.1MPagand 487 at BMCR condition. There is a pressure reducing station in the sootblowing system

The sootblowers are suitable for fully programmed operation or individual operation.

The blowing sequence can be optimized by the operator in such a way that the

overall sootblowing period is reduced to a minimum.

Taking into consideration the maximum prevailing flue gas temperature at the place

of installation, retractable blowers or rotating blowers may be used.

Long-retractable, part-retractable or rotating steam sootblowers are arranged on two


sides of the rear pass for cleaning the high temperature superheater, low

temperature reheater and economizer surfaces.

1.4 Main Equipment of CFB Boiler

1.4.1 Economizer

The economizer located in the rear pass consists of two (2) banks of 42 spiral-finned tubes, which adopt two runs and in-line arrangement. The material of

tube is 20G.

Normal anti-abrasive methods are adopted to protect economizer tubes. Plates are

installed at the inlet of the ECO around the flue to make the gas distribute uniformly.

Feedwater enters the lower inlet header and flows upward through the outlet header,

and is piped to the feed end of the steam drum.

1.4.2 Steam Drum and Drum Internals

The steam drum is located in front of the upper furnace and across the width of

furnace. The steam drum serves as a container of series of steam-water separaters

and a water reservoir for the steam generation circuits. The drum contains

steam/water separating equipment and internal piping for distribution of chemicals to

the water, for distribution of feedwater and for blowdown. The inside diameter of

steam drum is 1600mm, and the straight section of its shell is 12.3m long.

1.4.3 Furnace

The furnace is a 17170mm width 7492mm depth combustion chamber consisting

of front, rear, side waterwalls and split waterwalls.

At the bottom of the furnace, the front wall splits to form both the plenum floor and the

fluidized bed grid floor. Together with side walls, they form the water-cooled air

plenum. The water-cooled air plenum is lined with refractory to protect the tubes from

being eroded 870 high temperature gas. The grid floor is made up of internal


ribbed tubes (82.55) plus flat bar. Nozzles are fixed on the bar to insure the uniform distribution of the primary air and the bed materials and at the same time, to sweep

coarse solid particles and sundries toward to the discharge port. The elevation of the

grid floor is 7000mm.

The furnace is divided into lower, middle and upper part. The longitudinal section

view of lower furnace is trapezoid-shaped as the lower front and rear wall intersects

with the horizontal plane at an angle of 72 . The tube spacing for front wall (and roof), rear wall and side walls is 80 (60 tubes). Combustion occurres mainly in lower furnace, where the bed material is most dense and most active. Total air and fuel

needed for the combustion are sent to the combustor through this part. Besides the

primary air is induced through the grid into the lower part, the staged secondary air is

also fed in.

Six (6) fuel feed points and four (4) limestone feed points are located on the front wall

of the furnace. The middle and upper waterwalls are also made up of membrane wall.

At the top of furnace, the front wall bends toward the rear wall to form the furnace

roof which terminates in the upper header.

Abrasion resistance material is laid on the lower high density zone waterwall and split

waterwall. And it is also laid on all the areas near the gas outlet of upper furnace.

1.4.4 Cyclone

2 cyclones with internal diameter 7.5m are arranged between the furnace and the

rear pass. They are made of carbon steel sheets lined with refractory material. The

upper part is columnar, and the lower part is coniform. Gas outlet (vortex finder) is of

columnar plate structure with open ends. Gas and solid is separated in the cyclone.

The clean gas leaves the cyclone through the vortex finder and the solids enter into

the material recycle equipment directly to be fed into the furnace again.

The vortex finder is made of RA-253MA, anti-abrasive high strength steel.

Purge air nozzle are located in the inlet duct of cyclone to avoid ash buildup during

low load operation or shutdown. The purge air is stopped when the boiler is operating


under normal condition. Purge air is from boiler compressed air.

1.4.5 The Rear Pass

The rear convection pass has a 11811mm6350mm section. The upper part of the rear pass is made up of enclosure wall superheater. The rear shaft is divided by the

middle enclosure wall into two sections (the front flue and the rear flue). Here, the

bottom elevation of enclosure wall is 36040mm, below which the rear shaft is clad

with steel plates. The rear pass houses the horizontal banks of air heater, convection

economizer, LTS, HTS and LTR.

All enclosure walls are connected through inlet and outlet headers. The rear pass

front wall top tube spacing is increased from 127mm to 381mm to form a flue gas

inlet passage. The front and rear wall top tubes bend toward the middle wall to form

the rear shaft roof. The tube specification of the front, middle, rear walls and side

walls is 51, and the specification of hanging tubes for the front and middle wall screens is 63.5.

1.4.6 LTS

LTS is located in the lower rear flue of the rear shaft, and consists of 92 pieces of

dual loop horizontal tubes (51) arranged in line across the width of the boiler (counter to the gas flow).

The bank is fixed on the enclosure wall through the fixture and expands together with

the enclosure wall.

Normal anti-abrasive methods such as wearing plates are adopted to protect LTS

tubes. The distribution plates are also installed at the inlet of LTS around the flue to

make the gas distribute uniformly.

1.4.7 Primary Desuperheater

The primary spray water desuperheater is located in the steam connecting pipe

between LTS outlet header and PSH inlet header. The desuperheater is equipped


with a mixing liner and spray water piping. The liner is installed at the downstream of

the spray piping to protect the desuperheater shell from thermal shock. Instruments

are installed in spray water piping to measure the water flow and the water

temperature ahead of the desuperheater.

1.4.8 PSH

PSH (8 pieces) is arranged at the upper furnace near the front wall. PSH is

membrane wall construction with tube spacing of 63.5mm. Each platen consists of 43

tubes (12Cr1MoV, 51). Below the elevation 23715mm, the platen superheater is lined with refractory. The whole platen superheater expands upwards.

An outlet header (325) is located at the elevation 43666mm.

1.4.9 Secondary Desuperheater

The secondary spray water desuperheater is arranged in the steam connecting pipe

between PSH outlet header and HTS inlet header located at the rear wall of the rear

shaft. The superheated steam temperature is further controlled by the secondary

desuperheater. The construction of secondary desuperheater is basically the same

as that of the primary desuperheater.

1.4.10 HTS

Steam from the secondary desuperheater flows through connecting pipe into the

HTS, which is located at the upper rear flue of the rear shaft. The steam is introduced

into two ends of HTS inlet header and after flowing across HTS tube banks (counter

to the gas flow) goes into HTS outlet header, and then flows into the main steam pipe

from the two ends of the outlet header.

HTS is located in the upper rear flue of the rear shaft, and consists of 92 pieces of

dual loop horizontal tubes (51) arranged in line across the width of the boiler (counter to the gas flow), which is divided into two banks (HTS1 and HTS2).


1.4.11 Reheater Emergence Desuperheater

The reheater emergence desuperheater is located in the upstream of LTR inlet

header to protect RH from excessive high temperature. The desuperheater is similar

to SH desuperheater. Instruments are installed in spray water piping to measure the

water flow and the water temperature ahead of the desuperheater.

1.4.12 LTR

LTR is located in the front flue of the rear shaft, and consists of 92 pieces of trinary

loop horizontal tubes (51) arranged in line across the width of the boiler (counter to the gas flow).

The bank is fixed on the enclosure wall through the fixture and expands together with

the enclosure wall.

Normal anti-abrasive methods such as wearing plates are adopted to protect cold

reheater tubes. The distribution plates are also installed at the inlet of the cold

reheater around the flue to make the gas distribute uniformly. The first row of tubes

facing the gas is covered by wearing plates.

1.4.13 Reheater Micro Spray Desuperheater

The reheater micro spray desuperheater is located in the steam connecting pipe

between LTR outlet header and PRH inlet header, which is used to regulate reheater

steam temperature together with gas dampers. The desuperheater is similar to SH

desuperheater.

1.4.14 PRH

PRH is arranged at the upper furnace near the front wall, which consists of 4 pieces.

PRH is membrane wall construction with tube spacing of 89mm. Each platen

consists of 29 tubes (76mm). Below the elevation 28782mm, PRH is lined with refractory. The whole PRH expands upward.


The specification of its inlet header is 508mm, and the specification of its outlet header is 457.2mm.

1.4.15 Air Heater

The air heater adopts horizontal, in line and four-loop arrangement, which is located

in the lower part of the rear shaft. Air flows inside the tubes while gas flows outside

the tubes.

For each loop, 1-1/4 inch tubes are adopted to its upper two rows of tubes and the

right and the left sides of tubes, the other tubes are 40mm tubes. Q215-A tubes are used for the upper three tube banks, and 09CuPCrNi-A tubes are used for the lower

part of the fourth bank

The transverse spacing and longitudinal spacing of each tube bank are 80mm and

60mm respectively. The primary and secondary tube banks are arranged in two

parallel lines. Each two tube banks are connected by air duct to form two

independent paths. The primary air and the secondary air are supplied by

independent fans, and they go through their air ducts and heated by the flue gas

which flows across the tube banks. The primary and secondary air ducts are of

double inlet and outlet configuration and arranged along the width direction of the

boiler. The air temperature at the outlets is 290 .

1.4.16 U Valve

The solids from the cyclone flow through U valve seal device. There are two U valves

which are arranged below the cyclone and supported on the beams of boiler steel

structure. The expansion joints are located between the cyclone to U valves and U

valves to the furnace. U valves have two functions: one is to reinject solids into

furnace continuously and steadily to realize the balance of materials; the second is to

provide sealing between the cyclone (negative pressure) and the furnace (positive

pressure).

The outlet duct of each U valve is divided into two parts. So the solids from each U


valve return to the furnace by two passes, ensuring that the solids return evenly.

The power source of solids reinjecting is from the pressure difference from gap of

solids levels between the vertical leg and reinjecting leg of U valve. Besides the

proper air distribution by the bottom plenum, the vertical leg is equipped with five (5)

layers of aeration nozzles for fluidizing solids in order to ensure that solids are

reinjected back to the furnace continuously and steadily. The fluidizing air for U valve

is supplied by the separate blowers with high pressure and small flow.

The vertical leg is equipped with pressure-measuring instrument. By means of

controlling the pressure differences, the solids level is strictly controlled so as to

prevent the furnace gas from back-flowing into the cyclone during pressure pulsating.

The start-up bed material inlets are arranged at the reinjecting leg of U valve.

Emergence discharge ports are located at the bottom of U valve, which are used for

maintenance and emergence condition.

The shell of U valve is made of steel plates. The inner diameter of U valve is

1510mm. To prevent the abrasion due to the gas current with high temperature and

high-density dust, U valve is lined with anti-abrasion and refractory materials.

1.4.17 Ash Cooler

On the rear wall of the furnace, two rolling ash coolers are arranged. Part of the spent

bed materials comes to the bottom of the furnace and are then drained to the ash

coolers through solids transfer pipes. The drain openings of the bottom ash in the

furnace are located at the elevation of 7196mm.

The installation and maintenance of ash cooler are shown in INSTALLATION AND

MAINTENANCE MANUAL provided by the ash cooler manufacture

1.4.18 Ignition System

Two kinds of start-up ignition equipment or over-bed ignition and in-duct ignition are

adopted for this boiler. 6 pieces of over-bed heavy oil burners with heat input of 15%


rated load are located on both the side and rear walls of the lower furnace. 4 pieces

of in-duct burners with heat input of 15% rated load are located in the primary air

ducts below the water-cooled air plenum.

The in-duct burners for startup heat the primary air to 870. Then the hot primary air heats bed materials through air distribution device to ignition temperature. High

energy ignitor and flame scanner is provided for the burner.

1.4.19 Abrasion proof and refractory materials

Abrasion proof and refractory materials are required in all DONGFANG CFB boilers

to ensure the safe and reliable operation of the boilers.

Some parts of the CFB boiler are not pressure parts and are not cooled by the

circulating water and/or steam, but they are exposed to high temperature and high

velocity flue gas. These parts include typically cyclone, U valve etc., which are not

designed with heat transfer surface. So their inside surfaces are lined with two or

three layers of abrasion proof and refractory materials. The layer nearest to the outer

metal plate is insulating layer; the layer facing the gas is an abrasion-resistant layer.

Experience has shown that erosion in a CFB boiler can be reduced through proper

design of pressure parts and abrasion-resistant refractory coverage in key areas.

Abrasion-resistant and refractory materials selected for the protection of pressure

part also have low insulating characteristics, so the heat transfer and boiler

performance are not affected excessively. Refractory coverage of pressure parts in a

CFB boiler is primarily in the furnace. These areas include:

Lower furnace The lower part of the furnace is considered as the portion that has

the highest density of bed material. The bed material is mixed with incoming fuel and

limestone and fluidized by the grid nozzle airflow. The smaller particles are entrained

in the upward flow while the bigger particles fall back to the grid floor. The particles in

this area have very abrasiveness. So abrasion-resistant and refractory materials

shall be laid from the grid floor to the juncture of the vertical wall and the bevel wall in

the combustor. Abrasion-resistant and refractory materials are laid on both the side


walls (including split wall) near the furnace outlet.

Penetrations and discontinuities CFB boiler operating experience has shown

that erosion in the many locations of the furnace will not occur if there are no

discontinuities that would change the flow direction of the particles in the furnace.

Thus, the system is designed to eliminate unnecessary discontinuities. In the

locations where discontinuities must exist, such as platen surface penetrations and

the measure openings on the furnace, proper protection measures shall be taken

such as shielding or refractory coverage, or a combination of several protection

methods.

Furnace flue gas outlet This area is subject to high velocity flue gas with bed

material, so proper protection measures shall be taken to prevent the tubes in this

area from being eroded.

1.4.20 Boiler Steel Structure

The boiler steel structure is of bolted and welded construction and full enclosure

arrangement. There are eight (8) main columns for supporting boiler. The columns

are connected to the foundation at the elevation of -500mm by reinforcing bars.

Horizontal beams and vertical supports are provided between the columns to

withstand the loads of boiler proper, wind and earthquake.

The major pressure parts of the boiler (steam drum, furnace waterwalls, rear pass

gas flue, etc.) are hung by hangers from the top plates. Other components of the

boiler, such as ash cooler, air heater, in-duct burner, cyclone etc. are all supported on

the horizontal beams or on the earth by supporting devices or reinforcements.

Platforms and stairs are located in the locations where maintenance or inspection

shall be performed during boiler operation.

1.5 Water Volumes Of Major Boiler Parts:

Part Name During Hydraulic test (m3) During Operation(m3)


Steam Drum 27.7 12.2

Waterwalls 87.3 87.3

Superheaters 35 0

Reheaters 44.2 0

Economizers 17.7 17.7

Total 211.9 117.2

Note: 1. The volume of waterwalls includes the volumes of downcomers, feeder pipes,

split waterwall and headers.

2. The volumes of superheaters, reheaters and economizers all include the

volumes of their headers and connecting pipes.


SECTION 2 SAFETY PRECAUTIONS AND PREPARATION

FOR OPERATION

2.1 SAFETY PRECAUTIONS

Safety is primary for any boiler operation.

The following descriptions are some of the general precautions which shall be

applied when a steam generator first comes into operation. They are intended to

supplement the experience and judgment of personnel in charge of operation and do

not cover all precautions which shall be observed.

The manufacturer has complied with the national code pertaining to the design and

fabrication of boiler. A newly erected unit, prior to being put into operation, must be

carefully inspected by the authority to assure that all components or parts accord with

the design requirements.

All boiler auxiliary facilities must be in the first class operating condition, and meet the

design operation conditions and can operate in accordance with the manufacturers

recommendations and instructions. Here is an initial start-up check list for boiler

auxiliary equipment.

NOTE

The following items shall be checked prior to start-up of the boiler.

1. All fans and blowers shall be operable. Lubrication systems shall be operable.

Equipment shall be able to operate within the allowable variation of vibration.

2. All dampers, controllers and actuators shall be subjected to internal and external

inspection. The boiler auxiliary equipment shall be operable under the full range of

operation conditions and shall be free of caking or jamming. It is confirm that all

dampers can actually move to the stipulated positions as per the control

requirements.


3. Ensure that the ash removal system is connected with the ash cooler and that the

ash cooler is well ready for operation.

4. All remotely operated valves and slide gates shall be operable, and their limit

switches shall be checked to ensure their proper installation, thus guaranteeing

the accurate position indications.

5. All conveyors shall be trial-operated to ensure their normal operation.

6. All flow elements shall be calibrated.

7. The over-bed/in-duct burners, flame detectors and interlocks shall be operable.

8. All thermocouples and pressure sensors shall be checked and calibrated to

ensure their normal operation.

9. All flues, ducts, pipes, chutes or conduits through which air, gas, water, steam or

solids flow shall be connected accurately and reliably.

10. All expansion joints shall be inspected to ensure that proper connections have

been made.

11. All dust catchers shall be checked to ensure their normal operation.

12. All electrical connections shall be inspected to ensure their proper erection and

good insulation.

13. The remote drum water level indicator shall be checked, comparing its readings

with the readings indicated by the local water level gauge. This process must be

done periodically.

z Before a new boiler is put into service, the following items shall be checked:

1. The local drum water level gauge must be installed and checked in accordance

with the drawings prior to preliminary operation. When the water level of drum is

below the lowest visible point of the water level gauge, the gauge shall be drained.

Whenever gauge maintenance or replacement is done, it is necessary to verify

that its drain is normal.


2. Blowdown pipeline for water level gauge shall lead to the safe zone and drain

valves must be closed. The water level gauge must properly illuminated so that

that the operators on the operating floor can observe its readings sharply.

3. All vent, drain and blowdown pipelines shall be accessible and properly

connected with a blowdown tank or shall lead to other safe locations so as to

ensure the safety of personnel.

4. Valves that are located between the drum and equalizer and water level gauge

must be in the full open position.

5. All safety valve gags and hydrostatic test closure plates must be removed and

these valves must be in good condition. The steam discharge pipes of safety

valves shall be arranged and supported in accordance with the safety valve

manufacturers recommendations.

6. Drum internals must be properly installed in accordance with the drawings to

assure that there is no steam bypassing the internals.

7. All test interfaces, as deemed necessary, must be installed.

8. A leak test shall be conducted for the steam generators air and flue gas systems,

and all leaks shall be eliminated in accordance with Paragraph 2.8.

9. Heat emission zone of the boiler shall be insulated or roped off to ensure the

safety of personnel.

10. The thermal expansion of equipment shall not be disturbed by the temporary

scaffold, ladder, fragment and any construction material left.

z In addition to the above, the following items shall be thoroughly checked each time before operation:

1. All necessary operating instruments, both permanent and temporary, must be

installed and correctly calibrated, and be able to operate reliably.

2. All areas must be sufficiently illuminated to guarantee the safety operation of


boiler.

3. All hazardous barriers shall be cleared away. Unobstructed walkways and

platforms as well as ladders or stairways shall be arranged in the locations where

operation and observation are performed.

4. Air and gas passages must be unobstructed and can be thoroughly purged by the

circulating air of the unit.

5. The boiler feedwater must be ample, uninterrupted and qualified once the unit is

put into operation.

6. An ample and reliable fuel /limestone supply shall be available.

7. All access and observation doors must be closed after it is ascertained that no

one is inside the unit.

8. Drum manholes must be closed and sealed properly.

After it is assured that the above precautions are fully understood and have been

complied with, subsequent operations such as Drying Out, Boiling Out, Initial

Starting and Normal Starting can be initiated.

2.2 HYDROSTATIC TESTS

The steam generating unit shall be subjected to a hydrostatic test after the erection of

pressure parts is completed. A hydrostatic test shall also be made upon the

completion of each general overhaul or any repair affecting pressure parts of the unit,

or at any time when it is desirable to perform leak inspection.

CAUTION

THE BOILER TO BE TESTED SHALL BE FILLED WITH TREATED

WATER.

If the unit is not to be put into service after the hydrostatic test, proper treatment shall

be done, namely 200300ppm hydrazine plus sufficient ammonia or morpholine is used to raise the pH to 10. If the unit is to be put into service within a short time, the


treatment may be done as per the normal operation procedures. It is strongly

recommended that the unit be filled with the demineralized water or condensed water

for the test.

If the inventory of demineralized water or condensed water is limited, certain parts of

the unit may be filled with treated potable water or other water free of corrosive and

suspended materials. This water is not to remain in the unit for wet storage because

only demineralized water or condensed water can be used for wet storage.

For the test of drainable parts, the water with chloride content of less than 50ppm and

temperature of less than 52 may be used. But these parts must be subsequently be rinsed with condensed or demineralized water prior to operation.

The standard Supervision code for safety technology of steam generation boiler,

issued by the Labor Ministry of the Peoples Republic of China, specifies that the unit

shall be subjected to a hydrostatic test prior to the first operation or upon the

completion of any repair or change of pressure part. The hydrostatic test of the

primary water-steam system covers most pressure parts including superheaters,

furnace and economizer (as a whole), and its test pressure is 1.25 times of the drum

design pressure. The hydrostatic test of the reheat steam system, also called the

secondary steam system, covers LRH and PRH, and the test pressure of the reheat

steam system is 1.5 times of the inlet working pressure of LRH. The water

temperature of all hydrostatic tests is 2070 and shall be higher than the ambient temperature. Before applying a hydrostatic test to the unit, a thorough internal and

external inspection shall be done to ensure the completion of the following items:

1. All sundries and tools have been removed.

2. No one is inside the unit.

3. The manometer has been correctly calibrated and erected on the drum outlet

piping, with valves open.

4. Any part which is designed not to withstand the hydrostatic test pressure is

properly isolated or blanked off from such pressure.


5. All valves are operable and in the right position.

6. All steam system spring hangers are pinned in the fixed position.

7. All safety valves are gagged; all power actuated relief valves are decoupled.

After the foregoing items have been carefully checked:

1. Verify that drum manholes are properly closed.

2. Close stop and check valves, all drain and blowdown valves and other valves for

any gage or other internal equipment which is designed not to withstand the

hydrostatic test pressure.

3. Open the vents on the highest point of each component or part of the unit.

4. Be sure that the water will not be frozen during test and the unit will not be

subjected to freezing conditions following the hydrostatic test.

5. If during hydrostatic test, the water temperature is above 50 , it is necessary for the operators close to the unit to be careful in order to avoid the possible scald

from water leakage.

6. Check that only authorized personnel are in the vicinity of the unit to be tested.

When starting to fill the unit with water, the water temperature shall be close to the

metal wall temperature of the drum. The temperature of all other pressure parts shall

not be less than 20 .

CAUTION

WHENEVER THE HYDROSTATIC TEST PRESSURE EXCEEDS

5.1MPa, THE MINIMUM DRUM METAL WALL TEMPERATURE

AND WATER TEMPERATURE20MUST BE OBSERVED TO INSURE THAT THE HYDROSTATIC TEST IS PERFORMED ABOVE

THE BRITTLE TO DUCTILITY TRANSITION TEMPERATURE FOR

THE METAL.


z To obtain this hydrostatic test temperature, the following procedures are recommended (items 1 and 2).

1. If the boiler in-duct burner system cannot function, as may be the case for the

initial operation, any of the following methods (1), (2) and (3) is recommended.

(1) Use an external thermal source to heat so that the recommended

minimum temperature is obtained, as indicated by the drum surface

thermocouples.

(2) Use small oil and/or gas guns aimed through doors or resting on the grid

nozzles to raise the temperature to the recommended one. The boiler

tubes shall be kept away from the flame.

(3) If the medium temperature in the drum is below 20 , saturated steam may be fed into the drum through the drum blowdown or chemical feed

pipes to heat the water and the drum shell to the required temperature.

When the drum water level reaches the normal operating level, the

water shall be heated to a temperature 2 5 more than the recommended temperature so that the final water temperature will not

be below the recommended minimum temperature.

2. If the boiler in-duct burner system can function, the following procedure is

recommended:

(1) After the unit water level reaches the normal water level, the in-duct

burners are ignited to raise the drum temperature to 25 more than the recommended temperature.

(2) Switch off the in-duct burners and continue to fill the unit with water, and

at the same time inspect the drum drain pipelines and manholes for

leaks. Close the vent valves when water pours out of the vents located

at the highest points of the unit.

(3) Raise the pressure to the test pressure slowly. The recommended rate of

pressure rise shall not exceed 0.3MPa per minute to avoid the


occurrence of excessive pressure fluctuate.

(4) If the hydrostatic test pressure exceeds the design pressure, it is

necessary to reduce the pressure slowly. When the pressure is equal to

the operating pressure or the design pressure, the unit shall be

thoroughly inspected for leaks only at operating or design pressure. After

this inspection is completed, release pressure slowly at the

recommended rate of pressure release (not exceeding 0.3MPa per

minute), and open the vent and drain valves. Superheater system must

be thoroughly drained.

(5) If temporary manhole gaskets are used during the initial hydrostatic test,

they are to be replaced with proper gaskets before refilling the unit for

operation.

(6) Remove gags from safety valves and pins from spring hangers after the

test has been completed.

2.3 SOLIDIFYING REFRACTORY MATERIALS

All refractory materials shall be cured solidified and dried at the field by the erection

company in accordance with the refractory manufacturers recommendations to

assure that their actual performances meet the relative requirements.

2.4 BOILING OUT

2.4.1 General

Boiling out is a process to remove oil and grease inside the unit, and the cleaning

medium is usually a strong alkaline solution.

The presence of even very thin films of oil or grease or their decomposition products

on the boiler heating surfaces will seriously retard heat transfer. This film acts as a

dangerous heat insulating film and retards the rapid transmission of heat from the

metal to the boiler water. The resultant increase in metal temperature may cause


overheating and blistering of boiler tubes and even burst of tubes at high loads.

During the boiling out process, the gage glass may become badly discolored and

permanently etched. Our suggestion is that the customer has spare gage glass

fittings on hand. All the inoperable gage glasses shall be restored after boiling out

and chemical cleaning and before refilling the unit with water. The ordering and

replacement of gage glass shall be based on the manufacturers instruction.

The chemical shall be dissolved in water before being fed to the boiler and shall

never be fed to the boiler in the solid form. When handling corrosive materials, it is

necessary to ensure that the eyes, skin or clothing of the operator are bespattered by

them. When mixing these materials, it is recommended that goggles, rubber gloves

and cotton clothing be employed.

The chemical solution shall not be fed to the boiler in high concentration through the

regular chemical feed system because the high concentration solution may block up

the chemical feed piping and valves.

If the chemicals for boiling out must be injected to the boiler drum through the

chemical feed system, the solution concentration in the mixing tank shall be diluted,

namely 5% ahead of the chemical feed pump suction, and the pump and chemical

feed pipelines shall be flushed thoroughly after the pumping is completed.

2.4.2 Recommended Chemicals for Boiling Out

Alkaline chemicals such as soda ash and caustic soda are commonly used for boiling

out because these agents possess the ability to saponify the oils and greases to form

a soap compound that is easily removed through high pressure blowdown during the

boiling out process, and after the completion of boiling out, the unit shall be flushed

with cold water through a high pressure hose.

Phosphate (trisodium phosphate and disodium phosphate, accompanied by either

caustic soda or soda ash) may also be used as an agent to thoroughly clean the

internal surfaces of the boiler. In this connection, an embrittlement inhibitor and a

commercial wetting agent shall be added in the boiling-out solution.

Doc.No.: 39J

Documents

DEC CFBC Boiler Manual