Efficient production process
GIKIL‘s Coke Plant uses “by-product recovery“ technology. The production process starts by finding out what types of coking coals are suitable to produce the quality specifications of coke required by the client. The quality and proportions of different coals in the blend influence heavily the quality of the coke. Nevertheless, there is some degree of substitution. The objective is to minimize raw materials cost subject to the coke specifications constraint. Coking coal is shipped by rail from the port of Ploče to the storage areas in Lukavac. Then it is transported by a computer-controlled system of conveyors to the handling area where several types of coking coal are blended based on quality demand. The blended mixture is conveyed to the top of the coking batteries. Each battery consists of 65 ovens, which are refractory bricks-enclosed structures. The ovens are heated by using purified Coke Oven Gas produced by Cooking process. Coal is charged into the ovens from the top by Charging car and further heated to over 1000 °C in the absence of oxygen for 16 to 19 hours for Met Coke and 24 hours for Foundry Coke. Cooking process drives off the volatile materials while fixed carbon and residual ash are fused together. Volatile substances create Raw Coke oven Gas (COG). Raw coke oven gas is collected through an off-take system and purified on by-product unit. During purification process, Ammonia, Benzene, Sulphur, Coal Water & Crude tar will be extracted and the remaining cleaned Coke Oven gas is used to ignite the coke ovens and for fuel elsewhere in the plant. GIKIL in particular, will use the gas for steam power generation in its in-house power plant.
Process Flow: Diagram for Coke Plant
Hot coke is pushed from the coke ovens into a special railroad car after
the cooking process is completed. The car moves the coke to the quenching tower
at the end of the battery where it is cooled by decarbonized water. After that
the coke is screened to a uniform size. Coke sized 25 mm - 80 mm is suitable
for BFs in steel production. Size 10-25 is used by sintering plants to produce
sinter, which is subsequently fed into BFs. The finished product can be either
stored or shipped directly by rail.
The by-products of most commercial significance are crude Benzene, Ammonium Sulphate, crude tar.
Less important by-products are coke breeze and "other coke". Coke breeze consists of the fine screenings that result from the crushing of coke. "Other coke" is coke, which does not meet standard size requirements. Both other coke and breeze can be sold to non-steel producers.
The coking facilities consist of two batteries (IV and V with rated capacity of 0.7 M mt per year each). Each battery has 65 ovens, which are continuously operated on a three-shift schedule. Total plant rated capacity thus amounts to 1.4 M mt per year. Both batteries were designed by the Russian company Giprokoks and are operated by an electro-mechanical system. Battery V was delivered just before the start of the war and was not commissioned at the time. Battery IV had consistently reached 100% of rated capacity, but was stopped during the war and has not operated for the last 21 years. Both batteries were well protected and suffered no damage during the war. Battery V was commissioned in July 2004 and will be able to operate without substantial downtime for capital repairs over the next 10 to 15 years. It is estimated that it will take about 10 months to refurbish and restart battery IV. The longer repairs will eliminate the need for capital repairs in the next 10 years. Management believes that given the necessary financing, the battery will come online within 10 months of funds draw-down. Current experience makes it safe to assume that 90% of production will comprise high-grade metallurgical coke. At full capacity the two batteries are projected to produce 290 million cubic meters per year of coke oven gas. Quality specifications of raw materials and final output are regularly monitored by the plant laboratory while some samples are also sent to an independent third party laboratory.
The capacity of the servicing Coke chemicals plant matches the coking capacity of the plant. Purpose of the By- product unit is cleaning of the raw Coke Oven gas with task to remove highly valued materials like Crude Tar, Benzene, Ammonia. After treatment, gas is ready to be used internally for Battery heating and for Power production in GIKIL‘s Power Plant. By-product plant can produce at full Battery production 28,336 tonnes per year of crude tar, 8,586 tonnes per year of crude benzene and 6,000 tonnes per year of Ammonium Sulphate and 2,500 tonnes per year of naphthalene by washing 299,460 million Nm3 of coke oven gas. Cleaning process starts by primary cooling of the gas when Crude tar has been separated from the rest of Crude COG. Raw COG pass through Electrostatic Tar precipitators to remove all residual solid impourities. Continiuous motion of the COG has been ensured by gas exhausters. Raw COG is finally cooled down before washing. First stage of washing is by demineralised water with aim to remove Ammonia and partially Sulphur. This Ammonia water will be processed at Ammonium sulphate plant where final product will be Ammonium Sulphate. Second stage of washing is with Washing oil with aim to extract Benzene from Raw COG. Washing oil with absorbed Benzene will be processed at Benzene distillation unit where we will separate Crude Benzene from washing oil which will be returned to the washing process. After last washing process, gas is ready for use and is called Pure COG.