The Air Combustion Plant (ACP) is a cylindrical design, 250 kWth downfired pulverised fuel combustion system with interchangeable coal/ biomass burners, fuel (coal/biomass) feeding system, a dedicated air metering skid, flue gas filter, heat exchanger, and a temperature and flow monitored water cooling system for the combustion vessel and flue ducts.
The plant is operated using a dedicated control system connected to an industry standard SCADA system in a central control room for system monitoring, operation and data acquisition.
Lower floor of the rig (from left: Oxyfuel skid, air skid, gas heater controllers, bottom of combustion vessel, fuel feeding system. control PLC)
The 250 kWh Air Combustion Plant forms part of pilot-scale equipment at PACT facilities. It is a down fired, cylindrical design rig, operated at 120-350 kWth; typically 250 kW. The rig is a highly instrumented with state of the art analytical capability enabling detail combustion research including flame visualisation and modelling. It has dedicated coal and biomass burners and operates on pulverised fuel (coal/biomass/co-firing) or on natural gas and can be used for fuel testing and system optimisation for different types of fuels and fuel combinations. The plant flue gas duct is connected to the onsite PACT Solvent-based Carbon Capture Plant enabling post-combustion capture research with different fuels and under different combustion conditions. The rig also forms the core part of a 250 kW Oxyfuel Combustion Plant and in combination with a dedicated gas mixing facility it can be operated in various modes form Air to O2 enriched air to oxyfuel combustion.
- Conventional combustion research with state of the art analytical capability to enable flame visualisation and modelling for combustion system design, development and optimisation.
- Fuel testing and system optimisation for different types of fuels and fuel combinations coal, co-firing and biomass combustion.
- Post Combustion Capture research: the rig flue gas is connected to a 1 tonne/day (150 kW equivalent) Solvent-based Carbon Capture Plant enabling post-combustion capture research with different fuels and under different combustion conditions.
- Air to oxy firing: the rig enables conventional air firing as well as research into O2 enriched air combustion for example for more difficult samples such as biomass; in combination with a dedicated gas mixing facility the rig can also be operated in simulated and full oxyfuel mode with Exhaust gas recirculation as a 250 kW Oxyfuel Combustion Plant.
The plant has a dedicated fuel feeding system; interchangeable coal /biomass burners; dedicated air and CO2/O2 metering skids; temperature and flow monitored water cooling system for the combustion vessel, flue duct and heat exchanger, candle filter and exhaust fan. The plant is operated and monitored using a local HMI connected to an industry standard SCADA system. The main components of the plant include:
- 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 2.5 m3 cylindrical combustion rig. The rig is constructed of eight 0.5 m sections and total height of 4 m. 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 280 kWth. 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 500 kWth 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 supply and preheating: Combustion air is supplied by a dedicated air compressor feeding a four-channel air metering skid. The primary air is connected to the 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 air skid is also interconnected to the Oxyfuel Gas Mixing System which forms part of the 250kW Oxyfuel Combustion Plant. This enables operation in enriched O2 atmosphere as well as oxyfuel operation. All air supply lines are fed though gas heaters enabling preheating of the combustion air to up to 270C.
- Connection to the SCCP: A tee in the exhaust duct provides connection to the PACT Solvent-based Carbon Capture Plant (SCCP) for Post Combustion Capture research. The plant is normally operated to generate excess flue gas and the system fan on the SCCP draws the required amount of flue gas to the capture plant with the remainder leaving through the site stack.
- Control and monitoring system: The plant is operated and monitored using a dedicated PLC with a local HMI. The PLC is connected to an industry standard SCADA system in a central control room for system monitoring, operation and 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:
- Laser diagnostics: Particle Image Velocimetry and 2D and 3D Flame Imaging probes
- Ellipsoidal Radiometer
- Analytical probes:
- Suction pyrometer
- Solid collection probe (ash sampling)
- Medtherm Heat flux probe
- 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, sampling and recording continuously.
- Servomex 2700 Combustion Gas Analyser
- SERVOFLEX MiniMP 5200 Portable Gas Analyser (CO2 and O2)
- Emissions monitoring: a GASMET FTIR industrial analyser is also used for 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.
- 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.
- 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: Prior to the introduction of pulverised fuel, the rig is preheated on mains gas to typically 800-1000°C. Air and gas are fed from the air skid and ignited using the igniter; filter fan maintains reduced pressure. The air supply can be optionally preheated using the gas heaters. At operating temperature the gas is turned off and the coal/biomass is introduced into the burner gradually. The fuel ignites as it enters the preheated combustion chamber. Air flow and coal feeding rate are adjusted to desired rating. Bottom ash is collected in the water tray, whilst the flue gasses are pulled through the water cooled ductwork to the heat exchanger, the filter unit and out the stack.
AdvantagesPilot 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.
- Integrated system for Post Combustion Capture: the plant is integrated with the PACT Solvent-based Carbon Capture Plant enabling integrated system research and system modelling and investigation of plant and system flexibility with different fuels and operating conditions.
- Oxyfiring: Capability of O2 enriched through to oxyfuel combustion on associated 250kW Oxyfuel Combustion Plant.
- 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.