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Energy from Waste (Gasification)
Project Background									Client: Planet Advantage Limited
Jessup-Bould Limited provided technical support to Planet Advantage Limited during the pre-design phases of this project which uses Enerwaste technology. The plant has now been constructed at Scotgen’s Dargavel site in Dumfries, Scotland.
Process Description
The plant is comprised of 2 waste processing and heat recovery streams with a common steam turbine driven alternator. Each stream has four gasification chambers sequenced to operating on a programmed cyclic basis and provide a constant flow of synthesis gas to a common (one per stream) oxidation chamber. When a gasification chamber becomes available the operator opens the hydraulically driven front and rear doors. The operator de-ashes the chamber by use of a front end loader with pusher tool onto the de-ashing conveyor at the rear of the chamber. When the chamber has been emptied, the operator closes the doors.
To charge the gasification chamber, the operator opens the hydraulically driven charge door in the roof of the chamber. The front end loader is used to charge the chamber with feedstock material. A top side operator monitors filling and advises the front end loader driver as required to achieve an even distribution in the chamber to the working level. On completion of charging, the operator closes the charge door. The operator initiates the chamber start up sequence. Provided that the temperature in the oxidation chamber is above the minimum required by WID (the Waste Incineration Directive), the sequence ignites the material in the gasification chamber using the gas oil fired burner. Flue gas generated during start up to flow through the refractory lined syngas duct to the oxidation chamber.
Once combustion of the feedstock has been established oil firing is terminated and the chamber undergoes sub-stoichiometric gasification. The resulting synthesis gas flows through the established route to the oxidation chamber. A temperature controller in the outlet duct from the chamber will vary the speed of the chamber’s dedicated gasification air fan to control the gasification reaction. Air for the process is drawn from within the process hall. Waste heat is recovered from the oxidation chamber flue gases by raising steam in a boiler. This steam is used in the common turbine alternator to generate electricity for house use and export to the grid. Condensate is recovered for reuse as boiler feed water. Flue gas leaving the boiler is cleaned by dry scrubbing with PAC / Sodium Bicarbonate and a bag filter. Continuous emissions monitoring is used to control to Sodium Bicarbonate dosing rate and to ensure that the plant meets regulatory requirements.							Courtesy of Enerwaste
Responsibilities
Technical discussions with prospective detailed engineering design contractors. Mass end energy balance verification (including site performance testing): Site Performance Testing Supply and modification of laboratory equipment for gas sampling. Gas sampling and analysis for mass and energy balance purposes.
The initial contribution to this project was the assessment of the nominated detailed design contractor. This mainly centred on resolving discrepancies in the mass and energy balances provided by the technology provider and those from the contractor. Although the contractor had undertaken gas sampling at a demonstration plant for batch-wise processing of waste in Iceland, they were not able to ascertain sufficient information to enable these data to be used for mass balance purposes. Subsequently JBL was commissioned to undertake another set of measurements. In the original set of tests, the contractor had arranged for around ten gas samples to be sent to the UK for analysis. Analysis in the UK was deemed necessary due to the lack of gas analysis facilities in Iceland. This was reported to have been an expensive exercise. As a result, JBL undertook on-site gas sampling and analysis using an Orsat apparatus procured by Planet and therefore available for their future use. The Orsat was deployed at site following a period of in-house training with a tailor made gas ‘cocktail’ and equipment modification in the UK. Training had shown that accurate results for CO, H2, CO2, O2 and CH4 could be consistently achieved with the modified apparatus. The availability of analysis ‘on-demand’ more than tripled the number of readings taken at the initial testing. Furthermore, a structured sampling and data logging procedure was prepared that enabled meaningful data to be acquired in order to derive a series of mass balances for each batch gasified. Although the demonstration plant had no other means of monitoring energy generated from the waste, these performance tests enabled the energy release rate to be calculated using mass balance results. Issues over this contractors quoted scope of supply meant that an alternative contractor was sought. JBL assisted with the technical assessment of Planet Advantages alternative contractors’ short list. Following appointment of the detailed design contractor, there followed a transitional period during which the findings of the site tests were reported and handed over for use in the detailed design.
Unit Operations Batch gasification chambers. Combustion. Fans. Boilers. Steam turbine / Condenser Dry flue gas scrubbing. Cooling tower.				Hazards (Site testing) Waste; combustible and pathogenic solids. Fuels (gas oil). Gases arising from process (CH4, CO, H2). Hazardous analytical reagents (Conc. H2SO4, KOH, NaOH, etc). Hot gases, surfaces and materials. Moving heavy plant. Rotating machinery. Liaison Prospective Detailed Process Design Contractors