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Jessup-Bould Limited |
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A S Jessup-Bould: Fluidised Bed Coal Gasification |
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OSC Process Engineering Limited (my employer
at the time) were licensed to market the British Coal industrial fluidised
bed gasifier. This was a low pressure spouted bed design based on the 12
tonnes coal throughput per day, semi-full scale, pilot unit at the Coal
Research Establishment (CRE) at Stoke Orchard near Cheltenham. The technology
was aimed at industries requiring significant amounts of fuel gas such as
industrial furnaces or kilns. OSC offered a series of standard design sizes up to 2 metres diameter which would be fuelled by coal and could be run as char or inert beds. Oxygen enrichment of the fluidising air was also available in cases where a higher calorific value gas was required. |
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During my period of employment with OSC I
was responsible for assessing which units and mode of operation would be most
suitable for a clients needs, taking into account the feedstocks available.
In some cases CRE performed bench scale pilot tests to predict performance
using different feedstocks. Some enquiries were for budget prices and
required a low level of technical involvement. For other more serious
enquiries I was required to produce more detailed schemes, for which I
prepared process flow diagrams, heat and mass balances, utility requirements
etc based upon one or sometimes more of the standard sized units. Part of my work included revising the standard OSC design based on the results of trials carried out at CRE. The process design work which I completed included P&IDs, equipment process data sheets and instrument data sheets. |
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Process Description
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Industrial grade coal (12 to 25 mm) is fed
overbed via two lock hoppers into the fluidised bed gasifier. Fluidisation is
achieved by forcing a mixture of air and steam through the bed. The air and
steam react with the coal to produce the fuel gas having a typical
composition as shown in the table below. Limestone is used to absorb sulphur which
would otherwise be present in the fuel gas. The gasifier is operated at around 980°C
with a fluidising velocity of between 1.5 and 2.0 m/s. Hot fines carried out
of the gasifier in the fuel gas stream are separated in a cyclone and
re-injected back in to the gasifier to increase the carbon utililisation
efficiency of the process. A small amount of bed material is removed to
prevent the accumulation of mineral matter. The hot gases leaving the cyclone are cooled
to reduce their volume and to raise steam for use in the gasification
process. Excess steam can be utilised on the industrial plant where the
gasifier is to be located. Cooled gases can be filtered or scrubbed to remove any residual particles from the gas before it is used. |
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Unit Operations Fluidised Bed Gasification
(Char & Bauxite bed). Fans. Cyclones. Steam raising system. Power generation (Gas
engine). Bag filtration. Dense & lean phase
solids conveying. Solids cooling &
mechanical conveying. Materials of Construction Steels; carbon, stainless,
hardened, lined. Refractory brickwork. Documents Produced PFDs & mass
balances. P&IDs. Process & instrument data sheets. |
Hazards Fuels (producer gas;
explosive / toxic). Dusts containing heavy
metals. Hot surfaces and
materials (eg Char). Liaison Technology provider. Other engineering
disciplines. Drawing office. Sales and proposals
departments. Estimating department. Clients. Commissioning
engineers. Suppliers. |