Chemical and Process Engineering
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A S Jessup-Bould: Coke Oven By-Product Plants
1985 to 1999	Process engineering and commissioning of a range of by-product plants and their unit operations.
Summary of Process
Foul coke oven gas resulting from the carbonisation of coal is cooled and cleaned in the byproducts plant to enable its use as a fuel gas. Coke works around the world use many different configurations and types of unit operations to clean the coke oven gas and recover certain saleable byproducts. A typical plant will however follow the process route described: Coke oven gas leaving the ovens is sprayed with "flushing liquor" to quench it from around 800 ^oC to 85 ^oC and to flush the resulting condensed tar to the "downcomer". Here the tar and liquor are separated from the gas and are themselves separated by decantation. The liquor is then re-used, with excess liquor, due to condensation of water vapour from the gas, being processed in an "ammonia still". Gas from the downcomer is further cooled to about 25 ^oC in a "primary gas cooler", which may be either an indirect or direct cooler. Here more tar is removed. From the primary cooler the gas passes through an "exhauster", which provides the motive force through the plant. More tar is removed by the centrifugal action of the exhauster, however a "tar fog" is still present in the gas. This is removed by passing the gas through "electrostatic tar precipitators". Some heat is gained in the exhauster and often a "secondary gas cooler" is used to cool the gas to prevent naphthalene being condensed out as a solid in the downstream "ammonia washing" process. The ammonia washers remove corrosive ammonia by scrubbing the gas with a weak ammonia liquor. The ammonia is readily absorbed by this aqueous solution. Ammonia is removed from the now "strong ammonia liquor" by stripping with steam in an "ammonia still". After the condensing out the steam from the still overheads, which are usually returned as reflux to the still, the ammonia gas is disposed of by incineration, catalytic destruction or sold as concentrated ammonia liquor. Coke oven gas from the ammonia washers is then scrubbed with oil to remove saleable aromatic components in the gas stream such as benzene, toluene and xylene. The scrubbing is carried out in the "benzol washers". Naphthalene is also removed by a similar process in a "naphthalene washer" as this prevents deposition in the gas system. The benzol and naphthalene are recovered by stripping with steam in the benzol and naphthalene stills. A proportion of the cleaned gas, around 40% is used to "underfire" the coke ovens. The rest is usually used as a fuel gas either on the associated steel works, or in a power generation plant.
Specific Responsibilities
Process Design. Lead Process Engineer. Commissioning Engineer
Achievements
Process engineering responsibility secondments in USA and Africa.
Unit Operations Coke oven gas cooling (direct & indirect). Ammonia liquor pumping. Tar decantation & pumping. Electrostatic tar precipitation. Gas scrubbing (removal of Ammonia, Benzol, Naphthalene). Stripping (of Ammonia, Benzol, Naphthalene). Incineration & catalytic destruction of Ammonia. Ammonium sulphate production. Heat exchange & condensation. Materials of Construction Carbon & stainless steels. Duplex steels. Titanium. Hastelloy. Graphite. Documents Produced PFDs & mass balances. P&IDs. Process & instrument data sheets. Operating manuals. Training manuals.				Hazards Carcinogens (PAHs, benzene). Explosive process gases. Highly flamable byproducts. Poisonous process gases. Corrosive process liquors. Hot surfaces and materials. Heavy moving battery machinery. Liaison Other engineering disciplines. Drawing office. Sales and proposals departments. Project management. Estimating and procurement departments. Clients. Commissioning engineers. Suppliers. Standards etc. BS 5345 - Hazardous area classification. Internal working instructions. Commissioning plan. Site safe working procedures.