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 Propane Pre-Cooled Mixed Refrigerant Process Pillarella, M. 2010. PAPER PS2-5: The C3MR LIQUEFACTION CYCLE: VERSATILITY FOR A FAST GROWING, EVER CHANGING LNG INDUSTRY
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 interstage 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 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. Direct drive to compressor for refrigerant loop
OTSG vs Drum-Style HRSG HRSG OTSG LM6000 Installation overall size comparison
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 Thin wall tubes & mechanical design 409SS & 316SS Liners CS, 409SS, & 316SS brazed fins Allows dry running capability up to 1100 F (593 C)
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 Parameter Target Value Water Cation Conductivity (μs/cm) ph (stainless piping) (CS piping) Dissolved Oxygen (ppb) (stainless piping) (CS piping) <0.25 8 to 8.5 9.3 to 9.6 <300 <7 Iron (ppb) <10 Copper (ppb) <2 Total Organic Carbon (ppb) <100 Hardness (ppb) <1 Sodium (ppb) <6 Chloride (ppb) <6 Sulfate (ppb) <6 Note: Typically, the water quality required in gas turbine injection applications is more stringent than the OTSG FW spec. Silica (ppb) <20
Typical Condensate Handling Diagram
SCR IMPLICATIONS
Typical Layout of OTSG w/ SCR & CO Note split tube bundle SCR Module Distribution Grid (if req d) Catalyst Loading Platform CO Catalyst
Location of SCR Catalyst 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.)
SCR CATALYST REACTIVITY
OTSG Design Implications with SCR Catalysts 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.
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 Fin Material 409SS, 316SS and spacing Tubesheets <1050 F Chromoly 1050 1400 F 347SS 1400 1500 F NO6617 Steam Headers P22 or P91
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 Propane Pre-Cooled Mixed Refrigerant Process Pillarella, M. 2010. PAPER PS2-5: The C3MR LIQUEFACTION CYCLE: VERSATILITY FOR A FAST GROWING, EVER CHANGING LNG INDUSTRY
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 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 +65 o C. 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 600 o C). 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. Courtesy of the Linde Group
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 Tube bundle before insertion into the pressure vessel shell Courtesy of the Linde Group
COIL-WOUND HEAT EXCHANGER 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. Courtesy of the Linde Group
COIL-WOUND HEAT EXCHANGER Courtesy of the Linde Group
COIL-WOUND HEAT EXCHANGER PLATE-FIN HEAT EXCHANGER Courtesy of the Linde Group
Questions?