Heat Recovery Systems and Heat Exchangers

in LNG Applications

Landon Tessmer

LNG Technical Workshop 2014

Vancouver

Presentation Overview

• LNG plant arrangement with heat recovery

(OSMR Process by LNG Limited)

• HRSG/OTSG Introduction

• Design considerations in waste heat

recovery behind compressor drives

• Duct Burners

• LNG Cold Box Heat Exchangers

OSMR LNG PLANT ARRANGEMENT

4 Major LNG Technologies

• APCI (SMR, C3MR, AP-X, DMR).

• SHELL (DMR, PMR).

• LINDE (MFC).

• AXENS (LIQUEFIN).

SIMPLIFIED C3MR CYCLE

Pillarella, M. 2010. PAPER PS2-5: The C3MR LIQUEFACTION CYCLE: VERSATILITY FOR A FAST GROWING, EVER CHANGING LNG INDUSTRY

Propane Pre-Cooled Mixed Refrigerant Process

Possible LNG Plant Schematic – Optimized Single Mixed Refrigerant Process by LNG Limited (Perth, WA)

OSMR – Optimized Single Mixed Refrigerant Process

OSMR Explained

• The process is based on a simple single mixed refrigerant cycle but the performance is significantly enhanced by the addition of conventional combined heat and power technology and conventional industrial ammonia refrigeration.

• The heart of the process is a very simple single mixed refrigerant cycle which consists

of a suction scrubber, compressor, after-cooler and cold box. It uses a standard single stage centrifugal compressor which does not require a gear box, helper motor or inter-stage components as do most other LNG plants.

Major differences from Typical LNG Cycles: • GT waste heat recovery to produce power. • GT inlet air cooling using ammonia. • Pre-cooling of Mixed Refrigerant (MR) using ammonia. This is successfully used in a

small LNG plant in Western Australia. Since the cold box is a very simple design with minimal streams, the addition of ammonia to cool the MR from ambient temperature down to around 0C only, is not technically challenging.

HRSG/OTSG INTRODUCTION

AND

DESIGN CONSIDERATIONS BEHIND

COMPRESSOR DRIVES

Heat Recovery OTSG

for Power Generation

Direct Fired OTSG for

Enhanced Oil Recovery

Purpose of the heat recovery

OTSG

Direct drive to compressor for refrigerant loop

OR

OR

Direct drive to compressor for refrigerant loop

LNG plant usually needs steam as heating media for acid gas removal unit and reboiler duties for fractionation, therefore cogeneration cycle application will contribute the plant efficiency.

OTSG vs Drum-Style HRSG

LM6000 Installation – overall size comparison

OTSG

HRSG

Courtesy of

HRSG vs OTSG Drum-Type HRSG

Fixed Sections

OTSG Type HRSG

Non Fixed Section

Design Considerations - Metallurgy

• Incoloy 800/825 tubing designed to mitigate the following

failure modes:

– Dew point corrosion (water/acid)

• Allows cold feedwater to 60°F (17°C)

– Flow assisted corrosion

– Thermal shock

– Creep/fatigue failures

– Cycling/daily start – stop

– 409SS & 316SS Liners

– CS, 409SS, & 316SS brazed fins

– Allows dry running capability up to 1100°F (593°C)

Thin wall tubes & mechanical design

Bundle Growth – Thermal Cycling

Blue – hot/expanded condition Black hidden – Cold condition Note the tubesheet movement, tube growth, and flex tubes Makes the OTSG ideally suited for cycling application as stress and start up time are minimized compared to a traditional drum-type boiler.

Typical OTSG P&ID

OTSG and Plant Feedwater

Treatment

• No blowdown so water quality is critical (~50 ppb TDS)

• Requires demineralized and polished feedwater.

– Cation Conductivity Limit: 0.25 μS/cm

• IST recommends stainless FW piping from polisher to OTSG (particularly for cycling plants)

• Eliminates:

– Tube scaling

– Deposition and carry over

– Active chemical treatment

OTSG Feedwater Specification Parameter Target

Value

Water Cation Conductivity (μS/cm)

<0.25

pH (stainless piping)

(CS piping)

8 to 8.5

9.3 to 9.6

Dissolved Oxygen (ppb) (stainless piping)

(CS piping)

<300

<7

Sodium (ppb) <6

Chloride (ppb) <6

Sulfate (ppb) <6

Silica (ppb) <20

Parameter Target Value

Iron (ppb) <10

Copper (ppb) <2

Total Organic Carbon (ppb)

<100

Hardness (ppb) <1

Note: Typically, the water quality required in gas turbine injection applications is more stringent than the OTSG FW spec.

Typical Condensate Handling Diagram

SCR IMPLICATIONS

Distribution Grid (if req’d)

SCR Module

Typical Layout of OTSG w/ SCR & CO

CO Catalyst

Catalyst Loading Platform

Note split tube bundle

• SCR catalyst is located in the appropriate gas temperature zone for maximum efficiency

• Dual range catalysts have peak

efficiency at ~750 to 775F. Maximum continuous temperature is 950F (with reduced efficiency)

• OTSG bundle is designed to balance temperature exposure of catalyst in all operating scenarios (ie. unfired, fired, turndown, etc.)

Location of SCR Catalyst

SCR CATALYST REACTIVITY

• Cross-section enlarged to offset increased gas-side pressure drop (SCRs can add ~4”WC)

• Reduced fin pitch below dew points – particularly if liquid fuels burned in gas turbine (ammonium bisulphate concerns)

• In traditional low temp catalysts, start up times are prolonged in an effort to maintain low temperatures at the catalyst face.

• Cost impact is roughly +$2.5M for a ~50MW gas turbine OTSG install and 80%-90% NOx conversion on the catalyst.

OTSG Design Implications with SCR Catalysts

DUCT BURNERS

Supplementary Firing

• In LNG Plants duct burners may be used to consume: pipeline gas, lean gas, treated regen gas, or vaporized HC condensate. All to add to the available energy for heat recovery

• Common in cogen applications where the value of the steam exceeds the cost of additional fuel burned

• Natural gas is piped through “runners” and distributed by nozzles across the width of the duct.

• Scope consists of runners, gas distribution manifold, fuel handling skid (may need separate skids depending on range of fuel

compositions), and auxiliary blower skid

Supplementary Firing – Velocity Distribution

Supplementary Firing – Velocity Distribution

• Distribution Grid + Flow Straightener

• Flatten velocity profile and remove swirl

• Target 75 ft/s normal operation

• 35 ft/s minimum

• ±10% of average free stream velocity after distribution grid

• Burner duct length provision

• 1.5x flame length

• Burner duct liner material

• 409SS, 304SS, 316SS, Piro Block

Supplementary Firing – Velocity Distribution

• Typical temperature distribution guarantee +/-10% of the average temperature given a particular velocity profile input guarantee

• Typical heat release from a burner runner is 3 MMBtu/hr per liner foot

• Increase total heat release by wider duct or more runners (taller duct)

• Duct size is driven by a balance between space required for runners (heat release) and the 75 ft/s target

Module Material Considerations in Fired Applications

Tubesheets <1050 F – Chromoly 1050 – 1400 F – 347SS 1400 – 1500 F – NO6617

Steam Headers P22 or P91

Fin Material 409SS, 316SS and spacing

Fin Material Considerations

Design Limits CS < 454 C 409SS < 593 C 316SS < 871 C Corrosive duty must be considered as well

MAIN CRYOGENIC HEAT EXCHANGER (MCHE) /

“COLD BOX” HEAT EXCHANGERS

NG LIQUEFACTION TECHNOLOGY IS

BASED ON TWO PRIMARY HE DESIGNS:

MAIN CRYOGENIC HEAT EXCHANGER

SIMPLIFIED C3MR CYCLE

Pillarella, M. 2010. PAPER PS2-5: The C3MR LIQUEFACTION CYCLE: VERSATILITY FOR A FAST GROWING, EVER CHANGING LNG INDUSTRY

Propane Pre-Cooled Mixed Refrigerant Process

Possible LNG Plant Schematic – Optimized Single Mixed Refrigerant Process by LNG Limited (Perth, WA)

PLATE-FIN HEAT EXCHANGER

Courtesy of the Linde Group

PLATE-FIN HEAT EXCHANGER

Courtesy of the Linde Group

PLATE-FIN HEAT EXCHANGER

Courtesy of the Linde Group

• Brazed plate-fin heat exchanger is stack of alternating flat and corrugated plates. The corrugations form the flow channels for the process fluids (up to 10 fluids)

• Typical materials are aluminum alloys 3003 (blocks) and 5083 (attaching components).

• Maximum operating temperature is roughly +65oC.

• The fins/corrugated plates are serrated or solid (more heat transfer area but higher fouling + pressure drop with serrated)

• Fabricated using vacuum brazing (vacuum furnace at 600oC). Plates have filler metal cladding rolled on both sides. Attachments such as half pipes are welded.

• Results in a light-weight compact design

• AVOID: thermal shocks, large delta T (in mediums), dirty fluids, cyclic loads.

PLATE-FIN HEAT EXCHANGER

Courtesy of the Linde Group

COIL-WOUND HEAT EXCHANGER

Courtesy of the Linde Group

COIL-WOUND HEAT EXCHANGER

Courtesy of the Linde Group

COIL-WOUND HEAT EXCHANGER

Courtesy of the Linde Group

Tube bundle before insertion into the pressure vessel shell

COIL-WOUND HEAT EXCHANGER

Courtesy of the Linde Group

• A tubular heat exchanger but the bundle does not consist of straight tubes.

• Long length, small diameter tubes are wound in alternating directions around a centre pipe (the mandrel)

• The complete tube bundle is inserted into a pressure vessel shell. Every tube starts and terminates in tubesheets which are integral in the pressure vessel shell

• The shell-side distributes the 2-phase steam over the whole cross section of the tube bundle.

• Shell material is typically aluminum alloy 5083 and the tubes are a special grade aluminum allow as well. There are also CS and SS variants.

• It is a flexible bundle that can withstand much higher temperature gradients than a plate-fin design.

COIL-WOUND HEAT EXCHANGER

Courtesy of the Linde Group

Courtesy of the Linde Group

COIL-WOUND

HEAT

EXCHANGER

PLATE-FIN HEAT

EXCHANGER

Questions?