Ethane Cracker

A typical ethane cracker has several identical pyrolysis furnaces in which fresh ethane feed and recycled ethane are cracked with steam as a diluent. Figure 3-12 is a block diagram for ethylene from ethane. The outlet temperature is usually in the 800°C range. The furnace effluent is quenched in a heat exchanger and further cooled by direct contact in a water quench tower where steam is condensed and recycled to the pyrolysis furnace. After the cracked gas is treated to remove acid gases, hydrogen and methane are separated from the pyrolysis products in the demethanizer. The effluent is then treated to remove acetylene, and ethylene is separated from ethane and heavier in the ethylene fractionator. The bottom fraction is separated in the deethanizer into ethane and fraction. Ethane is then recycled to the pyrolysis furnace. 

Traditional olefin plants have more than one alias. One is even fraudulent. They are variously called ethylene plants after their primary product steam crackers because the feed is usiuilly mixed with steam before it is cracked or whatever aacker, where whatever is the name of the feed (ethane cracker, gas oil cracker, etc.). Olefin plants are sometimes referred to as ethylene crackers, biit only those who don t know any better, use that misnomer. Ethylene is not cracked but rather is the product of cracking. 

Olefin plants all have two main parts the pyrolysis or cracking section and the purification or distillation section. The ethane cracker in Figure 5—2 has a pyrolysis (from the Greek, pyros, fire) section that consists of a gas-fired furnace where the cracking takes place. The newer individual furnaces can each handle more than 400 million pounds per year of ethane feed. 

In the purification section of an ethane cracker, the gas can be handled in one of two ways. In order to fractionate the streams, they must be liquefied. Since they are all light gases, liquefaction can be done either by increasing the pressure in a compressor or by reducing the temperature to very low points in something called a cold box. The ethane cracker in Figure 5—2 shows the compressor option. (Even then, the streams have to be cooled to assure they liquefy.)... 

It may seem curious that an ethane cracker has propane and heavier included in the outturns. There are two reasons. The ethane used as feed is rarely pure. It generally has a couple percent of propane and heavier-in it that results in a small amount of heavier products. But why bother or go to the expense to get pure ethane feed In the first place, the olefins plant purification section can handle them. Secondly, some heavy hydrocarbons are actu-... 

The separation section of a gas oil cracker looks like a small refinery, as you can see in Figure 5 or in Figure 5—5. In addition to the fractionators and treaters used in the purification section of the simpler ethane cracker, there are facilities to separate the heavier coproducts. In the front end of the separator facilities in Figure 5-4, the cold box option for handling the liquefaction of the gases is shown. Temperatures as low as -220°F are achieved in this super-refrigerator. At those low temperatures, Freon wont do the job. Liquid air, methane, ethylene, or ammonia are often used as the refrigerant in much the same way Freon has been used in an air conditioner. 

Can push natural gas production up and free ethane for ethane cracker... 

Asia-Pacific companies are likely to base their investment decisions on similar criteria. Participating in Middle East production is certainly attractive in some areas, especially ethane crackers and ethylene production. China is not self-sufficient in crude oil or natural gas and must import them, or the end products. This... 

Consumers can also negotiate with feedstock suppliers on upfront payments or payment terms under which they pay a higher price than the lowest market price at the trough, but pay lower prices when product prices spike. An interesting application of this is the potential for an ethane cracker operator to convert the economics of its cracker to those of a virtual naphtha cracker, by paying an integrated gas producer-processor a price for ethane indexed to naphtha-based ethylene production costs. 

The capital cost of a 500,000 t/y ethane cracker is 718 million (2007). The non-feedstock operating costs are taken as 10% of the capital per annum or 71.8 million per year (MM /y). If the plant is built in three years on the basis of a 20 year life with a DCF rate of 10%, annual return on capital, as detailed in the Appendix, is 14.4% or 102.8MM/y. 

This order of magnitude estimate is based on a hypothetical plant for the production of 500 kt/year of ethylene with a capital cost of 150 million. This is compared to the cost of a green-field ethane cracker of about 700 million. Process selectivity is assumed 100% with operating allowance for feed and fuel of 5.5% and 3% respectively. 

Steam cracking of ethane is the most widely used process for making ethylene. U.S. 6,578,378 (to Technip-Coflexip) gives a typical ethane cracker product composition and describes an improved separation process for ethylene recovery. U.S. 5,990,370 (to BP) gives yields for ethane, propane, and mixtures. U.S. 5,271,827 (to Stone Webster) gives details of furnace design and yields for a naphtha feed. Several other separation schemes for ethylene and propylene recovery are described in the literature. Estimate the cost of production for a new steam cracking facility that produces 1 million metric tons per year of ethylene and 600,000 metric tons per year of propylene. What feedstock would you recommend ... 

As a consequence of the more ordered and compact structure, the volume contractions due to the dehydrogenation and dealkylation reactions of carbon deposits from ethane crackers are less important. The deposit maintains a limited void fraction, the density is higher and decoking process is more difficult. 

The front-end hydrogenation corresponds to a front-end deethanizer for an ethane cracker or a front-end depropanizer for the heavier feedstocks both are placed at the third-stage discharge of the cracked-gas compressor. 

For an ethane cracker, a single demethanizing stripping system operating at medium pressure is implemented the overhead is recycled back to the cracked gas compressor. 

Fig. 1. Progressive separation applied in Front-end hydrogenation for an ethane cracker.

Commercial plants Currently, one integrated DCC and ethane cracker is in operation in Rabigh, Saudi Arabia. A CPP unit has recently started up this year in Shenyang, China. There are three DCC units currently in design, with planned startup dates in 2011. 

Figure 1 schematically represents an ethane cracker with horizontal coils. Two coils are running in parallel through the furnace. The coil length in the radiant section is 95 m. The length of the straight portions of the coil is S.85 m, the length of the bends 0.55 m. The radius of the latter is 0.178 m. The internal diameter of the tube is 0.108 m. The ethane feed f>er coil is 68.68 kg/m -s. The ethane is... 

PI2.4 At high temperatures, ethane dissociates via the reaction (ethane cracker)... 

The ( 247.16 million) expansion project, known as EP2 (Ethane Cracker Expansion Project 2), was first commissioned in July 2007 to increase production of ethylene, used as a feedstock in the manufacturing of plastics, to cater for the increased worldwide demand especially fi om emerging markets. 

The problem QAPCO faced later on was that while its Ethane cracker plant in Qatar yielded 75% ethylene only a small percent of the remaining 25% feedstock effluent was recovered. Most was burnt off in the flare or incinerator. 

To overcome these monumental challenges, QAPCO forged new links with Qatar s national gas processing company Qatar Petroleum, and a number of its subsidiaries including SEEF, a linear alkyl benzene producer, and Q-Chem, another ethane cracker operator, to get them involved in the recovery process of the effluents. 

In 2009/2010 QAPCO introduced the advanced processing of byproducts as part of its EP2 project at its ethane cracker plant to turn waste hydrocarbons into commercial products, cut greenhouse gas emissions improve operational margins increase commercial opportunities with subsidiaries and substantially reduce the amount of hydrocarbon streams wasted in the incinerator or flare. 

Most of the ethylene produced by the ethane cracker is consumed in the low density polyethylene plants run by QAPCO and our affiliate company Qatar Vinyl Company (QVC). The rest is exported to our overseas customers. 

Downstream, there will be two separate polyethylene units, one downstream of Kellogg-Tyssen naphtha cracker and the other downstream of Petronas joint-venture ethane cracker both of which will be capable of producing high density polyethylene (HDPE) and linear low density polyethylene (LLDPE). As for polypropylene there may be three separate plants, namely a 150,000 MTPY downstream of a naphtha cracker by Kellogg-Tyssen JV, a 80,000 MTPY downstream of a dehydrogenation complex by Himont-C.T. Chao JV the latter based on imported propylene. 

National Petrochemical Company (Iran) 2007 1 Mtpa ethane cracker established in the 9th olefin complex at Assalnyeh. 

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