Pilot Plant
State of the art control system
The Gasplasma pilot plant facility is comprehensively monitored and controlled via a SCADA (Supervisory control and data acquisition system) and remote viewing CCTV monitors.
Arrangement of the Gasplasma facility
Belt conveyor system
A crane is used to lift containers of RDF into a receiving hopper. The RDF is then transferred to the feed hopper by a belt conveyor system.
Fluid Bed and feed system
The arrangement of the feed system and fluid bed gasifier (FBG) is shown in figure 3. The RDF is fed continuously at a controlled rate through a solid fuel feeder system. The feed rate is modulated by a variable speed screw feeder which discharges into a rotary solids valve (RSV), purged with inert gas, which provides an airlock on the system. The feed from the RSV is transferred via a constant speed feeder to the gasifier. The FBG contains a heated bed of calcined clay which is suspended in a rising column of gas. The fluidised bed technique enables good contact between the fuel and oxidant streams to achieve high gasification rates and close temperature control within the unit.
Gasifier and feed system
Oxygen and steam are injected in the base of the unit, and their rate is metered to match the feed rate of the RDF to maintain the temperature of the bed between 750-850°Celsius and generate a crude syn gas of the required calorific value. The oversized ash material generated in the FBG is also removed via a sealed valve in the base section.
Fluid Bed Gasifier base section showing Oxygen and steam injection and ash removal system
Plasma Convertor roof
The contaminated gas from the FBG is treated in the cylindrical plasma converter unit (roof of unit shown). The plasma arc is transferred from the tip of the drilled graphite electrode located in the centre of the unit, to the surface of the molten bath in the refractory lined converter hearth. The crude syn gas from the gasifier unit flows via a refractory lined duct through a port in the roof of the converter. Steam and oxygen injection also occurs at this stage, to enhance the cracking and reforming of the long chain organic species and promote the gasification of soot and char products. The plasma arc power to the unit is controlled to maintain the temperature of the gases exiting the unit to ~1,100-1,250°Celsius. The ash particulates entrained in the input gas stream drop out and are vitrified in the molten bath.
Scale Model
General View of Rear View
The 100:1 scale model of the Gasplasma plant, rated to treat 50,000 tonnes per annum of RDF (Refuse Derived Fuel) shows the general configuration and relative sizes of the main process equipment. The plant is compact; the footprint area of the covered space is 1,750m2 whilst the external space is 1,000m2. There are 4 main sections in the facility:i) fuel storage area, ii) advanced thermal processing section, iii) syn gas cooling and cleaning (external) and iv) Power island.
Gas Cleaning Plant
- Engine Exhaust
- Gas Storage
- Scrubber
- Waste Heat Boiler
- Particulate Filter
The plant has a 2 days fuel storage capacity to allow continuous operation of the thermal plant. A belt conveyor system is used to transfer and provide managed storage of the received RDF material. The advanced thermal treatment section incorporates 2 processing units: the fluid bed gasifier (FBG) and the plasma converter (PC).
The RDF is transferred at a controlled rate via a screw conveyor system to the FBG feed system. The feed incorporates an airlock to prevent gas egress or air ingress at this point. The feed is transferred at a controlled rate to the gasifier ~9 m high and 3 m diameter. The FBG operates at a temperature of between 800-900°Celsius and is fluidised by steam and oxygen injection at the base of the unit. The plasma converter is a cylindrical refractory lined steel vessel ~4metres high and 4.3 metres in diameter. The drilled graphite electrode is located in the centre of the unit and the plasma arc, which uses nitrogen as the plasma stabilising gas, is transferred from the tip of the electrode to the surface of the melt. In operation, the crude syn gas from the gasifier unit flows via a refractory line duct into the plasma converter. The high temperature within the converter, plus the addition of steam and oxygen addition at this stage, promotes the cracking and reforming of the long chain organic species and the gasification of soot and char products. The power to the unit is controlled to maintain the temperature of the gases exiting the unit to ~1,100-1,250°Celsius. Ash particulates carried over from the gasifier drop out in this section and are assimilated in the melt.
The cleaned syn gas (from the syngas cleaning system described in slide 3) is fed to the power island which incorporates gas engines. The power generated is partly used in the fuel preparation process but the major part is exported to the power grid. Around 6 tonnes per hour of 10 Bar steam is recovered from the engine exhaust gas stream for use elsewhere in the process or for additional electrical power generation.
Detail of Interior Plant
- RDF Fuel Storage
- Feed System
- Plasma Converter
- Fluid Bed Gasifier
- Gas Engines
The syn gas cooling and cleaning system is located outside of the building. The hot gas exiting the plasma converter is cooled from ~1,200 to 200 °Celsius using a waste heat boiler that generates ~4 tonnes per hour of 10 Bar steam for use elsewhere in the process. The contaminated dust entrained in the gas stream is efficiently captured in the particulate filter unit. A gas scrubber located downstream of the filter is used for the removal of acid gases. The cooled clean syn gas can then be stored in pressurised buffer storage tanks prior to use at the power island. The gas emissions from the gas engines are discharged through a low profile stack.
