Gasloop Guide

7/25/2019 Gasloop Guide

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Gas Loop

Gas Loop

Discuss the typical components of the gas loop using the prepared

schematic diagram.

Figure ----Schematic Diagram of Gas Loop

Combustion Analysis

Provide introductory statement. Use the complete data of the

selected fuel, to include ash, sediments and others. Present the results in

terms of weight and mass.

Sample computation

Ultimate Analysis

Carbon ( C ) 64%

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Hydrogen ( H ) 4%

Nitrogen ( N ) 1.4%

Sulfur ( S ) 1.2%

Oxygen ( O ) 6.8%

Ash, sediments

Computing the required O2:

Briefly discuss the procedure in computing the required oxygen.

For Carbon (C):

32

12x0.64=1.71

For Hydrogen (H):

32

4x0.04=0.32

For Sulfur (S):

32

32x0.012=0.012

1.71 + 0.32 + 0.012 = 2.042kg O

2

kgcoal0.068 =1.974

kg O2

kgcoal

Computing the Product of Combustion:

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Briefly discuss the procedure in computing the product of

combustion. Include in the computation the gravimetric and

volumetric analysis of the flue gas

For Carbon (C):

44

12x0.64=2.35

For Hydrogen (H):

18

2x0.04=0.36

For Sulfur (S):

64

32x 0.012=0.024

2.35 + 0.36 + 0.024 + 0.08 =2.814kg O

2

kgcoal

Prepare a table showing the summary of computed values

Combustion Analysis

Corresponding

Reaction

Required

O2

(include values in

terms of volume and

mass)

Product of

Combustion

(include values in

terms of volume and

mass)

C ~ C + O2CO2 1.71 2.35

H ~ 2H2+ O2 2H2O 0.32 0.36

N ~ Inert Gas Inert Gas 0.08

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S ~ S2+ 2O2 2SO2 0.012 0.024

O ~ --------------- -0.068 --------------------

TOTAL 1.974 2.814

Computation for Air-Fuel Ratio and Gas-Fuel Ratio:

For Air-Fuel Ratio:

Maf=1.974 + 1.974 (0.768

0.232)

Maf=13.07kg of air

kgof fuel

For Gas-Fuel Ratio:

Mfg= 2.814 + 1.974 (0.768

0.232)

Mfg= 15.85kgof flue gas

kgof fuel

Briefly discuss the procedure in computing the concentration of

various products of combustion here. Compare the results with the

existing emission standard (e.g. particulate matter, sulfur dioxide).

Results shall be used as basis in determining whether there is a

need to provide an air pollution control facility or not.

Air Preheater

Discuss the importance of air pre-heater and its function. Also

include the type/ kind of air preheater.

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Briefly describe each of the type/kind of air preheater focusing on

its major feature / components.

Types:

Tubular Type

Regenerative Air pre-heater

Rotating-plate regenerative air pre-heater

Selected Air Pre-heater

Briefly discuss type /kind of air preheater to be provided for the system

Air Pollution Control Facility and Management

Briefly discuss the type of pollutant that the plant would generate.

Cite the result of computation (flue gas concentration) and use it as basis

whether to provide control facility or employ appropriate management

measures to lessen it.

If pollution control facility is needed, discuss different type of

control facility and select which is more effective and economical.

Examples of control facility or measures are:

Electrostatic (Plate) Precipitator

Wet electrostatic precipitator

Baghouses

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Use of low sulfur fuel

Burner configuration/method of burning

Stack

Briefly discuss the function of stack. Cite importance of a properly

designed stack(economics , allow dispersion of pollutants)

Calculating Stack Height

Introductory statement:

Summary of operating conditions

Maximum continuous rate 1215 t/h of steam

Superheated steam pressure 17.2 MPa

Superheated steam temperature 541 CReheated steam temperature 541 C

Fuel bituminous coal

Tb= 353.33C + 37.78C

Tb= 391.11C

Where:

Tb= saturation boiler temperature,

Mfg= mass flue gas,

Mf= mass of fuel,

dfg= density of flue gas,

Qfg= volume flow rate of flue gas.

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Mfg= 15.85kgof flue gas

kgof fuel

Mf= 136.47

kgof fuel

sec

Compute individually for plants that have multiple generating units

(example if 3 units)

Mf= 136.47 / 3

Mf= 45.49kgof fuel

sec

dfg= 0.55kg

m3

Qfg=MfgPfg

=15.85

kg of flue gas

kgof fuel x 45.49

kgof fuel

sec

0.55kg

m3

Qfg =1,310.93m3/s

Use the recommended excess air

TypicalRanges of Excess Air Requirements for Various

Fuels and Methods of Firing

Fuel Excess air, % by

weight

Pulverized Coal 15 20

Fluidized bed Combustion 15 20

Spreader stoker 2535

Water-cooled vibrating grate stoker 2535

Chain and traveling grate stoker 2535

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Underfeed stoker 2540

Fuel oil 315

Natural gas 315

Coke oven gas 315

Blast furnace gas 1530

Wood/bark 2025

Refuse-derived fuel (RDF) 4060

Municipal solid waste (MSW) 80100

Source: Babcock & Wilcox, a McDermott company

Qfg= 1,310.93 x (excess air)

Qfg= ------- m3/s

Determine/calculate the draft every 30m of stack:

From PPE by Morse (pp.494);

D30=k (da- dg) 0.007578 da V

5

Q g

Where:

D = available draft per 30 m. of chimney

= cm. of water

k = 2.7 for brick of chimney and 2.4 for steel stack

da =density of air kg/m3

dg= density of flue gas kg/m3

V = gas velocity in the chimney m/s

Qg= gas flow in m3/s

D1= 0.004 V2dg

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Hchimney=Chimney Draft

D30

x 30

Computation for Height of Stack: (sample only)

For velocity

@ 6.1 m/s;(from PPE by Morse)

D30=2.4 (1.2kg

m3 0.55

kg

m3 ) 0.007578 (1.2

kg

m3

6.15

1,573.12

D30= 1.54 m

From PPE by (Morse, pp.496)

Hstack=0.004 (6.1 )2 (0.55 )+2

1.54x 30

Hstack= 40.56 m

Computation for Stack Diameter:

ID = 1.3

Q gV

ID = 1.3 1,573.12

6.1= 20.88 m

Repeat the procedure / calculate by assuming other values within

the range. Option is to have it in excel format for faster calculation.

Present the result in table form (sample shown below).

Computed Stack height and diameter at different velocity

(sample)

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Velocity

V

Height of chimney

H

Inside diameter

ID

Product

H x ID

6.1 m/s 40.56 m 20.88 856.08 m

2

11 m/s 46.25 m 15.55 719.19 m2

15.24 m/s 55.88 m 13.21 738.17 m2

The lowest value of the product is the ideal stack dimension

Fans and Blower

Introductory statement, which could include purpose of the

equipment and the need to provided one.

The design of fans and blowers would depend on the combustion

technology or type of the power plant.

For boilers with built-in burners, fan capacity need not be

computed. Just mention the type or capacity of the fan for supply air if

available in the specification.

Induced Draft Fan

Types of induced draft fan are as follows:

Centrifugal Fan

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Axial-Flow Fan

Briefly discuss the advantage and disadvantage of different type of

fan. Type of fan to be used should be justified.

Induced Draft Fan Computation

Figure ----shows the variations of air and the flue gas densities

with flue gas temperature.

(Source: PPD Morse, 1953)

Figure -----Variations of Air and Flue Gas Densities with Flue Gas

Temperatures

Sample computation :

Mg=15.85kg gas

kg fuel

Mf=136.47kg fuel

sec

For three (3) stack

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Mf= 136.47 / 3

Mf= 45.49kgof fuel

sec

Vfg=11ms(From stack design chosen for velocity of flue gas)

Pb=17.2Mpa (Super heated steam pressure from our boiler selection)

dg=0.55kg

m3

Qg=m ' g

dg,

But

m

m( f)( g)m' g=

where;

Qg=Volume flow rate of flue gas

mg= Mass flow rate of the gas

dg= Density of the flue gas

tfg= Flue gas temperature

tbsat= Saturation boiler

temperature

@ tfg=tbsat+100 F

tfg=tbsat+37.78 C

Pb=17.2Mpa ; tbsat=353.33 C (using steam table)

From figure 4.4, it shows that with a flue gas temperature of

391.11C, the density of flue gas is 0.55 kg/m3

tfg=353.33+37.78

tfg= 391.11 C

dg=0.55 kg

m3

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m

m( f)( g)m' g=

(15.85 )(45.49)

721.02 kg gas

s

Qg=721.02

0.55

Qg=1,310.93m

3

s

Qg=1310.93 (1.2 )

Qg=157312m

3

s

For volume flow rate, CFM

1573.12m

3

s x (3.28 ft1m)

3

x 60s

1min

3,330,925.12CFM

For total head, !"

!"=hs+h#

Velocity head, h#

h#=V

2

2 g

h#= (11)2

2(9.81)

h#=6.17m

h#=6.17 (1.2)(100)

1000

h#=0.74 cm $ater

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Static head, hs (typical values from PPD Morse pp. 477)

Boiler = 2.73

Super heater = 2.73,

Economizer = 2.54,

Air heater = 3.81,

Dust collector = 6.48

Note:

specify or use typical values of chosen dust collector or air

pollution control facility;

values would differ depending on the type of equipment used;

and use other data if available

hs=(2.73+2.73+2.54+3.81+6.48+2 )x 1.2

hs=24.35 cm of $ater

Therefore;

!"=hs+h#

!"=24.35+0.74

!"=25.0926 cm$ater

Select fan that is available in the market. Parameters to be used

in selecting should be volumetric flow rate and draft. Include picture of

the selected fan and no. of units to be used.

Concentration of Exhausted Flue Gas

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Briefly discuss the expected pollutants to be emitted by the plant

and the need of addressing it.

Dispersion Model ( derivation of formula used in estimating pollutants at variousdistance from the plant):

The Gaussian dispersion equations to calculate the chemical concentration

along the plume centerline at ground level and maximum ground level concentration

(MGLC) were used in the stud! The said equations were derived from the general

Gaussian dispersion equation (designated as equation ") which is given #elow:

C(x$$%)& ' exp"*+(*)

+

, -exp"*+(%.*%)

+

, / exp"*+(%/.*%)

+

,0 +%

where:

C& concentration of pollutants at coordinates x$$% (mg*m1)

'& emission rate of pollutants (mg*sec)

% & hori%ontal (crosswind) and vertical standard deviations of pollutants

concentration along the centerline of the flume (m)

& mean wind velocit (m*sec)

x & downwind distance along the centerline of the plume (m)

& hori%ontal distance from the centerline of the plume (m)

% & vertical distance from the ground level (m)

. & plume height (m)

To estimate the concentration along the plume centerline at ground level$

and % is #oth set equal to %ero! Thus equation " reduces to the following form:

C(x$2$2)& ' exp"*+(.*%)+, - equation +0

%

3quation + is further simplified # setting .&2$ which is used in estimating

MGLC (no thermal or momentum flux)!

C(2$2$2)& ' - equation 10

(%)2

where Cmax& maximum concentration of chemicals*su#stance (mg*m1)

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( %)2& hori%ontal and vertical deviations at x&2

4olving for emission rate of pollutant (') from equation 1 and su#stituting the

value of ' to equation +$ then the resulting equation is:

C(x$2$2)& C(2$2$2)(%)2 exp"*+(.*%)+

, -equation 50%

3quation 5 is then used in estimating the concentration of chemicals (Cx$2$2) at

distance (x) from the source$ along the plume center line at ground level! The

equation does not ta6e into account the dispersion of the air contaminants in the

crosswind direction (axis)! .ence$ it can #e expected that estimated values will #e

higher than the actual concentration!

7n using equation 5$ it is assumed that stac6 height (h) is equal to plume

height (.)! This assumption would li6ewise result in higher values$ as plume rise is

not considered! 8lume rise however$ could #e not so significant as the temperature

of the flue gas will #e much lower after passing a series of treatment! The

temperature of the flue gas is usuall lowered to the designed operating temperature

of the equipment!

The assumptions in using Gaussian dispersion equation should also #e

considered in the interpretation of data! These assumptions are: (a) wind and

velocit and direction are constant over height and over averaging period9 (#) the

emission rate is constant9 (c) the plume reflects completel at the ground (i!e!$ no

deposition)9 and (c) no diffusion occurs in the direction of the plume travel (La

Grega$"5)!

Calculated concentration of pollutants (sample only)

Formula estimating concentration at various distance from the plant;

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C= Q

%(Q& Qy)

Where:

C = pollution concentrationQ = emission rate, mg/s

(Q& Qy ) = horizontal and vertical standard deviation

= mean wind velocity (data based on Philippine condition)

Q = Qfg(concentration of pollutant; g/N.cm)

Qfg= use design data ; m3/s

H = ------ m (From Stack Height Design)

TSP = calculated concentration after control facility ;g/N.cm

Values taken from figure below:

(Q& Qy ) = horizontal and vertical standard deviation; taken from

figure below

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Figure -----Horizontal Dispersion Coefficient

Source: http://www.lenntech.com/

Figure -----Vertical Dispersion Coefficient

For Maximum ground level concentration (x=0;y=0;z=0)

Q&=6m

Qy=10m

C=

471.94

%(10) (6)(2)

C(000)= 471.94

%(10) (6 )(2)

= 1.25mg

m3

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Maximum ground level concentration:

@ x = 0;

(x00)=

C(000)(Q& Qy)e

[ 1

2(!Q&)2]

(Q& Qy)

(x00)=1.25 (6 )(10)e

[ 1

2 ( 46.256 )2]

(6 )(10)

= 1.24

mg

m3

= 1,240'g

m3

Table ----- shows the concentration of flue gas with respect to

distance from source.

Concentration with respect to distance

Distance,

In meter Qy Q&

g

m3

200 22 14 229.25

225 24 15 199.24

230 26 16 169.54

250 28 17 149.55

300 40 20 81.96

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The maximum ambient concentration of Total Suspended

Particulates (TSP) is 90 g/m3. Table ----- shows that the allowable

concentration will be met at 300 m away from the stack.

Gas Loop Summary

Summarized the gas loop components and update and show the

resulting / revise diagram indicating the number and specifications.

Figure ----Proposed Diagram of Gas Loop for---------Unit

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Gasloop Guide