Integrated Plasma Gasification Combined Cycle
Summary of major process blocks
Alter NRG Corp.’s gasifier is a critical component of an integrated plasma gasification combined cycle facility (“IPGCC”). The Air Products Tees Valley Renewable Energy facility is configured as an IPGCC. Plasma gasification can be used to produce syngas which can be conditioned and then converted to liquid fuels or power through technology platforms like fuel cells or reciprocating engines. For all of those applications, the majority of the plant, is dedicated to processing waste and making clean syngas, will be quite similar.
Plant Process Summary
MSW is delivered to the plant receiving facility which will have several days of storage capacity. The other two materials, coke and flux, which are fed into the gasifier concurrently with the MSW are also delivered to the facility. The flux material is typically crushed limestone and its purpose is to promote proper slag flow within the gasifier. The coke forms a bed within the reactor.
The three materials are metered onto a common charge conveyor which transports the feedstock to the gasifier. Depending on the size of the MSW, it may have to be shredded on site to a size less than approximately 15 cm before being transferred to the conveyor.
Within the gasifier, the organic portion of the MSW is converted into syngas. The syngas is partially quenched with atomized water at the top of the gasifier prior to exiting the gasifier at a temperature of approximately 850 °C through two nozzles.
The metallic and ash content of the MSW forms molten slag, which flows through the tapholes at the bottom of the gasifier. The slag is then quenched and granulated upon exiting the gasifier. The resulting vitreous granules are conveyed and loaded onto trucks for export to customers.
The gasifier is equipped with Plasma torch systems to ensure the internal temperatures in the reactor are sufficient to guarantee complete conversion of carbonaceous material to syngas and to melt all the inorganic material.
Syngas is cooled through a caustic venturi quench scrubber and scrubber system and then proceeds to a wet electrostatic precipitator (WESP). The primary purpose of the venturi quench and WESP is to remove the particulate matter entrained within the syngas as well as to convert chlorine within the syngas into salt. The cooled and particulate free syngas proceeds through a series of syngas cleaning processes to remove chlorine, sulphur, lead, cadmium, zinc and mercury. Intermediate compression and cooling steps remove moisture from the gas.
The clean syngas is then compressed in a multi-stage compressor and fed into a gas turbine to produce electrical power. The turbine flue gas heat is recovered by a heat recovery steam generator (“HRSG”). The steam from the HRSG is combined and fed to a multi-stage steam turbine to generate power.
Alternately, the cleaned syngas can be used in reciprocating engines to make power or it can be converted to liquid fuels using a number of available conversion technologies.
Example of IPGCC Plant Inputs and Outputs
An IPGCC plant that processes 1000 tpd of MSW (12 MJ/kg) will produce about 50 MW of power. It will also produce about 250 tpd of slag that can be sold as aggregate. A further 20 tpd of coarse particulate is produced which can be recycled back into the gasifier. The remaining 20 tpd of fine particulate, which includes elements like cadmium and mercury must be properly disposed of. In other words, an IPGCC plant that process 1000 tpd of MSW will produce only 20 tpd of residuals that require long term disposal. The other 980 tpd is converted into electricity and beneficial products.