The 250 kW Oxyfuel Combustion Plant (OCP) utilises the 250 kW Air Combustion Plant operated in an Oxyfuel mode whereby fuel is combusted in an atmosphere of CO2 and O2 rather than in air. This prevents nitrogen in the air generating flue gases with around 95% CO2 suitable (after processing) for geological storage or CO2 utilisation applications. In this mode the plant is operated with a dedicated Oxyfuel Gas Mixing System (OGMS) - an automatic high precision CO2 and O2 mixing skid, which provides individually mixed CO2 - O2 gas feeds, including high CO2/O2.
The PACT 250 kWth Oxyfuel Combustion Plant forms part of pilot-scale equipment at PACT facilities. Its base components are the same as for the PACT 250kW Air Combustion Plant with down-fired burner (Coal/biomass) and rig arrangement and similar thermal output range of 120-350 kWth. However, in the oxyfuel mode the plant also integrates a dedicated CO2/O2 gas mixing skid for operation in synthetic CO2/O2 atmosphere and O2 injection. This is further complemented by steam injection capability for wet and dry flue gas recycling and trace gas injection system (NOx, SOx,..) to individual lines for simulated combustion atmosphere. The plant can be operated in both real and synthetic Oxyfuel mode. The plant benefits form a high level of instrumented with state of the art analytical capability enabling detail combustion research including flame visualisation and modelling for combustion system design, development and optimisation.
- Oxyfuel combustion research
- Testing of wide range of fuels: coal, biomass, gas
- Air to oxy firing
The plant includes: fuel feeding system; interchangeable coal /biomass burners; air supply metering skid and CO2/O2 metering and mixing skids for synthetic Oxyfuel operation; temperature and flow monitored water cooling system, candle filter and exhaust fan flue gas recycling loop with O2 injection. The plant is operated and monitored using a local HMI connected to an industry standard SCADA system. The main components are detailed below:
- Burner: The burner is mounted on top of the rig. The plant is equipped with two dedicated interchangeable burners for coal (with up to approximately 20% biomass) and biomass. The coal burner is a scaled version of a commercial Low-NOx Doosan Babcock burner, with a primary annulus for introducing the pulverised coal and carrier gas, and swirled secondary and tertiary annuli to deliver the rest of the oxidiser. The burners have an internal air splitting system providing both secondary and tertiary air feeds from one air supply. The burner flame is ignited using a torch igniter. Once lit the LFL 1.335 provides natural gas burner flame safeguard control.
- Combustion vessel/rig: The plant is a down fired combustion system with an approximately 2.5m3 cylindrical combustion rig. The rig is constructed of eight 0.5m sections and total height of 4m. The inside of the rig is lined with a light-weight cement refractory an upper six section of the rig are double skinned and water cooled. This enables rapid heating and cooling for faster experimental throughput and provides better control of the combustion environment temperatures. The bottom of the rig is sealed with a water table. Combustion gases are discharged through the side of the bottom section into a flue gas duct.
- Exhaust gas duct and heat exchanger: Flue gases from the combustion rig are drawn through double-skinned, water cooled flue gas duct to a shell and tube heat exchanger. A bypass around the heat exchanger allows simple temperature control before the flue gas enters the candle filter.
- High temperature candle filter - Exhaust fan package. The filter unit is a ceramic candle filter and integrates the main combustion fan which maintains the rig at a reduced pressure. It operates at temperatures of up to 400°C and filters particles down to sub-micron sizes.
- Fuel feeding system: The plant has a dedicated gas metering skid rated for up to 280kWth. For pulverised fuel a dedicated coal feeder is used with up to 20% biomass. The pulverised fuel feeding system consists of two hoppers interconnected through a rotary valve, a screw feeder and a vibratory plate. This provides uniform loading into the feeder pipe. The feeder pipe is connected to a venturi feeder on the primary line, which pneumatically conveys the fuel to the burner.
- Cooling water system: The rig is connected to an onsite closed loop cooling system served by a 500kWth cooling tower. The water cooling system provides temperature control for the upper six sections of the combustion vessel, the flue gas duct, the heat exchanger and analytical probes. Water temperatures and flows are monitored and logged on individual feeding lines.
- Combustion air/oxidant supply, oxyfuel gas mixing skid and gas preheating: In air mode, combustion air is supplied by a dedicate compressor feeding a four-channel air metering skid. The air skid is interconnected to an Oxyfuel Gas Mixing System (OGMS), with both skids feeding air/oxidiser supply lined to the burner and rig. In simulated oxyfuel combustion, the oxidising gas is supplied by the OGMS fed from large onsite CO2 and O2 cryogenic gas storage tanks. The skid meters and mixes the CO2 and O2 inputs into four individually controlled lines feeding the oxyfuel rig. The OGMS provides capability to create the desired gas compositions including very high O2 or CO2. The primary supply line is connected to the burner via the fuel feeding system to pick up solid fuel; the tertiary line provides air to the windbox of the burner, and is split internally into secondary and tertiary air. The overfire line can be flexibly connected to different points in the rig. The secondary line on the OGMS feeds an O2 injection system installed on the Exhaust Gas Recirculation (EGR) line. All air/oxidiser supply lines are fed though gas heaters enabling preheating of the combustion air to up to 270C.
- Flue gas recycling loop for Full oxyfuel operation: A by-pass tee is installed in the flue gas duct after the filter fan for flue gas recycling (in full Oxyfuel mode). The offtake is fed back to the tertiary air/oxidise inlet of the burner via a tee connection. A fan is installed in the recycle loop to control the amount of recycled flue gas. O2 in the recycled flue gas is replenished from the OGMS via a pure O2 line feeding an injection and mixing spurge pipe.
- Control and monitoring system: The plant is operated and monitored using a dedicated Siemens PLC connected to an industry standard SCADA system in a central control room. The OGMS has a dedicated control system which is interconnected to the plant PLC for data acquisition.
- Analytical instrumentation and facilities: The plant is highly instrumented enabling detailed research and plant monitoring and control. The rig sections, flue gas duct and heat exchanger are fitted with thermocouples monitoring internal gas temperatures and water jacket temperatures. Flow meters provide cooling water flow data for energy calculations. Rig sections are equipped with ports for sampling of gases, pressure sensors and installation of analytical probes. Upper rig sections are also equipped with viewing ports and ports for state of the art Laser Diagnostics and 2D and 3D Flame Imaging, enabling detailed combustion research and collection of validation data for modelling. There are also provisions for ash deposition, and slagging and fouling studies. Associated analytical facilities include:
o Laser diagnostics: Particle Image Velocimetry and 2D and 3D Flame Imaging probes.
o Ellipsoidal Radiometer.
o Analytical probes:
- Suction pyrometer
- Solid collection probe (ash sampling)
- Medtherm Heat flux probe
o Flue gas analysis: Gas sampling in flame and flue gas exit;
- Dedicated flue gas analysers monitoring CO2 (both high and low concentrations), O2, NOx, SOx and THC concentrations in the flue gas outlet sampling and recording continuously.
- Servomex 2700 Combustion Gas Analyser.
- SERVOFLEX MiniMP 5200 Portable Gas Analyser (CO2 and O2)
o Emissions monitoring: a GASMET FTIR industrial analyser is also used for the monitoring of the above gases, THC components, water and other gases. A PERKIN ELMER SQ8 GCMS analyser is also available for analysis of gaseous samples.
o Particle size analysis: a CAMBUSTION DMS500 Fast particulate analyser is used for flue gas particle analysis with particle size, number and mass spectra in real time.
o Other analysis: Other analysis can also be provided through the extensive analytical facilities of the Universities of Leeds and Sheffield who jointly operate the PACT site.
- Mode of operation: Oxyfuel combustion utilises the PACT 250kW Air Combustion Plant but the fuel is combusted in an atmosphere of CO2 and O2 rather than in air to exclude nitrogen and generate CO2 rich flue gas. The plant can be operated in two modes:
o Full oxyfuel mode with Exhaust Gas Recirculation (EGR) where the CO2 from the exhaust gas is recycled back into the system. A tee in the flue gas duct after is connected to a recycle fan which draws a required proportion of the flue gas and injects it back into the tertiary line inlet on the burner. The oxygen consumed in the combustion process is replenished (in excess) from the secondary line on the OGMS by injecting directly into the recycle duct through a spurge pipe.
o Simulated Oxyfuel mode where rather than recycling the real flue gas, the OGMS feeds mixtures of CO2 and O2 to simulate the flue gas recycling. The OGMS can provide individually mixed CO2-O2 gas feeds, including high concentrations of CO2/O2. A dedicated steam package boiler provides steam injection capability for each of the lines line for wet/dry operation. A trace gas injection system is also available to simulate flue gas composition.
To operate in oxyfuel mode the plant is normally started in air combustion mode with mains gas. Once the combustion chamber is preheated, the changeover from Air to Oxyfuel mode can be achieved either before or after the addition of pulverised fuel. For real EGR the recycle fan is gradually turned up to complement or replace the tertiary air intake; the O2 feed from the OGMS to spurge pipe mixer in the recycle line is adjusted with the flue gas flow and its O2 concentration. In simulated mode the air supply on the air skid is turned gradually down while pre-selected mixtures of CO2-O2 gases are gradually increased from the OGMS until the oxidising gas is fully supplied by the OGMS.
- Pilot scale: the plant can be operated at 120- 350kW providing a cost effective and flexible bridge between lab scale research and large industrial pilot plants.
- Flexible combustion chamber heights: Adjustable combustion chamber height from 2.5m to 4.5 m (typical 4m) to suit experimental need.
- Oxyfuel operation: in synthetic (wet/dry and/or trace gas injection) and real Exhaust Gas Recycling mode
- Extensive analytical capability: enabling detailed combustion research and modelling including integrated system modelling.
- Expertise: managed and supported by leading UK universities and academic expertise in the area of combustion and carbon capture research, and system modelling.
- Open access: the facilities are open access to both industry and academia, for more cost effective utilisation
- Shared office facilities: the PACT facilities have shared office space both on site as well in PACT administrative offices nearby; these offices are open to visitors accessing the facilities during experimental work.