Overview

The 250kW Oxyfuel Combustion Plant (OCP) utilises the 250kW Air Combustion Plant operated in an Oxyfuel mode whereby fuel is combusted in an atmosphere of CO2 and O2 rather than in air. This avoids nitrogen present in air to generate flue gases with around 95% CO2 for 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 plant can be operated in two modes:

  1. full oxyfuel mode with Exhaust Gas Recirculation (EGR) where the CO2 comes from the exhaust gas recycled into the system with a make-up injection of O2 to enable combustion; and
  2. a simulated oxyfuel mode with gas feeds individually mixed and supplied by the OGMS.

The system can operate between the two modes at different degrees of EGR and with different O2 concentrations. The plant is also equipped with dedicated gas heaters for each of the lines and can be operated as a dry/wet EGR system whereby steam, generated by dedicated steam package boiler, is injected into individual lines after the gas heaters. There is also a dedicated NO2 injection system for simulated EGR.
The plant is operated and monitored using a dedicated PLC connected to an industry standard SCADA system in a central control room for system monitoring, operation and data acquisition. Oxyfuel Gas Mixing System has a dedicated control system which is interconnected with the main rig PLC for monitoring and data acquisition.

Example applications

  1. Oxyfuel combustion R&D with coal/biomass/co-firing utilising simulated to full Exhaust Gas Recirculation system
  2. Fuel testing and system optimisation with different solid fuels (coal/biomass/waste) and under different oxyfuel/oxy-air (enriched air) combustion conditions. 
  3. System modelling and optimisation complemented by state of the art 3D Laser Diagnostics and Thermal Imagining analytical capability for flame visualisation and analysis, and latest modelling software for combustion system design, development and optimisation. 
  4. Integrated system modelling for optimum ASU, combustion system and flue gas post-processing for different fuels

System description

  1. Main Fuels: Coal, biomass, co-firing, and natural gas (primarily for pre-heating).
  2. Combustion vessel: Down fired, 2.5m3 cylindrical design rig with eight sections of approximately 0.5m in height and total height of nearly 4m; rig sections are double skinned and water cooled.
  3. Burner: The rig is equipped with two dedicated interchangeable burners for biomass and coal respectively, which can be operated in oxyfuel mode.
  4. Oxyfuel Gas Mixing System (OGMS): A high precision gas mixing skid connected to large CO2 and O2 storage tanks; the skid meters and mixes CO2 and O2 inputs into four individually controlled lines feeding the oxyfuel rig. The primary line is connected to the fuel feeding system, where the carrier gas is mixed with pulverised fuel and fed directly to the burner on top of the rig. The tertiary line also connects directly to the burner and is then internally split within the burner to separate lines. The overfire line is connected the middle of the combustion rig. The secondary line feeds an O2 injection system on the Exhaust Gas Recirculation (EGR) line to replenish consumed oxygen in the CO2 rich flue gas. All lines are individually fed via dedicated gas heaters enabling preheating of gases before they reach the rig. The skid has a dedicated PLC, which is also integrated with the main oxyfuel plant PLC. The OGMS provides capability to create any gas compositions including very high O2 or CO2 mixtures.
  5. Steam Skid: The system incorporates a dedicated steam skid fed from a dedicated package boiler for wet EGR; steam to be injected into individual lines after the heaters. 
  6. Operating modes and Exhaust gas recycling: The plant can operate between two modes: real Oxyfuel mode with full EGR and a simulated mode:

a) In the simulated EGR mode, the OGMS provides required O2-CO2 mixtures to the primary, tertiary and overfire gas feeds. The mixed gases from the OGMS are fed through dedicated gas heaters to the rig. Optionally steam can be injected into any of the lines. Fuel is then combusted in a synthesised atmosphere of CO2 and O2. Flue gases discharged from the bottom of the rig are fed through a water cooled flue gas section through to a heat exchanger. Flue gas is cooled from approximately 700C to 400C before it is fed to a system filter to remove fly ash. The filter fan pulls the flue gases through the system and the speed of the fan is automatically adjusted by a pressure sensor on the combustion vessel.  Filtered flue gases are vented through the facility stack. The CO2 in the combustion flue gas can reach 95% CO2.

b) In the full EGR mode the CO2 comes from the exhaust gases which are recycled into the burner. A tee connection in the flue gas pipework after the filter fan is connected to a recycle fan. The fan draws a portion of the flue gas and pushes it through the recycle line back to the tertiary inlet in the burner. A specially designed mixing section injects O2 from the secondary line on the OGMS into the EGR line to makeup the depleted oxygen for further combustion of fuel. In conventional combustion flue gas contains around 13% CO2, 6% O2 and the remainder largely nitrogen. EGR increases the CO2 concentration in the combustion atmosphere by replacing nitrogen to generate flue gases with up to 95% CO2.
 

 

Analytical capability

The rig sections and flue gas pipework are fitted with thermocouples and a pressure sensor enabling full system temperature and pressure monitoring. The rig vessel is also equipped with sampling and injection ports for gas sampling, pyrometer and heat flux probes and visualisation ports for state of the art 3D Laser Diagnostics and Thermal Imaging facility enabling detailed combustion research and modelling. The system has a dedicated gas analysis systems enabling continuous online monitoring of the flue gas including high and low CO2 concentration. There are also provisions for gas injections, ash deposition, and slagging and fouling studies.

Associated analytical facilities include: