Steam cracking condensates

A steam cracker circulates a considerable amount of steam to dilute gases and lower their partial pressure (1 to 2 tons per ton of feed), A fraction of the steam condensed at 90 is drawn off and coalesced to treat the HC emulsion. It is then stripped of the gasoline carried over before being recycled to the LP process steam producer and pumped to preheat 

The blowdown of the closed system, called quenching water, often amounts to 15 to 30% 

This water is slightly alkaline (pH 8 to 9) and contains phenols (20 to 30 mg l ). In addition, there is the blowdown water from the boiler itself which is very alkaline (concentration of conditioning products) and saline, but several times smaller in volume than the condensates. 

No incorrectly or incompletely treated spent caustic must be reintroduced in the system as this would cause mineralization of the water and a rise in the mineral COD. 

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In a FCC condensate, the COD is due to sulfides and phenols, whereas in a steam cracking condensate, it can be due mainly to aldehydes and acetic acid-... 

Acecates occur in steam cracking condensates and in some formation water. 

Partial recycling of distillation condensates, stripped FCC condensates, or better yet by steam cracking condensates that contain fewer salts. 

Residues (petroleum), coker scrubber, condensed-ring-arom-containing Residues (petroleum), hydrogenated steam-cracked naphtha, atm tower, vacuum, light... 

The VPS overhead consists of steam, inerts, condensable and non-condensable hydrocarbons. The condensables result from low boiling material present in the reduced crude feed and from entrainment of liquid from the VPS top tray. The noncondensables result from cracking at the high temperatures employed in the VPS. Inerts result from leakage of air into the evacuated system. Steam and condensable hydrocarbons are condensed using an overhead water-cooled condenser. The distillate drum serves to separate inerts and non-condensables from condensate, as well as liquid hydrocarbons from water. Vacuum is maintained in the VPS using steam jet ejectors. 

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. 

UNS S30409) stainless steel (SS) for metal temperatures above 1,200°F (650° C). Caustic stress corrosion cracking (SCC) from solids can occur in the steam preheat coils if solid carry-over is excessive (see Chapter One, Steam and Condensate section). The inlet connections to the steam methane reformer furnace tubes are either IViCr-V Mo (1,100°F [595°C] maximum) or 21/4Cr-1Mo (1,200°F [650°C] maximum). 

Immediately after cracking, the cracked gases are reduced in temperature as quickly as possible to stop the cracking processes and prevent the cracked gases forming coke. This quenching is often referred to as the transfer-line-heat-exchange (TEE). Excess steam is condensed and the water recycled (not shown). Heat from the TEE is recovered as process steam. 

Metal granules also have been found in cokes formed or deposited on iron, cobalt, and nickel foils in experiments using methane, propane, propylene, and butadiene (7-10). Platelet-type coke, whose properties match those of graphite also was produced in some cases. Lahaye et al. (11) investigated the steam cracking of cyclohexane, toluene, and n-hexane over quartz, electrode graphite, and refractory steel. They report that heavy hydrocarbon species form in the gas phase, condense into liquid droplets which then strike the solid surface, and finally react on the solid surfaces to produce carbonaceous products. The liquid droplets wet and spread out on certain surfaces better than on others. 

Finally, it is relevant to observe that this dissolution presents strong analogies with a condensation process discussed and stressed by several authors (Cai et al., 2002) as being responsible for coke formation/deposition in the TLE tube outlet section at operating temperatures of 350 450°C. Indeed this mechanism can be explained on the basis of the solubility of heavy species of the process fluid phase in the soft polymer. There has also been research into the computer generation of a network of elementary steps for coke formation during steam cracking process (Wauters and Marin, 2002). 

Refineries that have access to isobutylene streams from steam cracking may face the problem that the existing alkylation and possibly catalytic condensation units cannot take the normal butenes which are contained in the pyrolysis stream. 

The current world production of ethene and propene is mainly covered by the petrochemical route based on steam cracking, that is, thermal pyrolysis of petroleum liquids (naphtha, gas oils) and natural gas condensates, that is, ethane, propane, etc. [13-15]. A schematic stoichiometry is given in Eq. (5.2). As an alternative, ethanol can be converted via catalytic dehydration to ethene, as shown in Eq. (5.3) [16]. For steam cracking of naphtha, the reaction stoichiometry gives a maximum product yield of nearly 100 wt%, whereas ethanol conversion can lead only to maximum yields of 61 wt%. 

Maleic anhydride (MA) is an important raw material in the production of alkyd and polyester resins. It was first obtained by Nikolas Louis Vauquelin in 1817, by heating maleic acid to over 140 °C. In 1905, Richard Kempf obtained maleic acid by the oxidation of benzoquinone. The first patents covering the production of maleic anhydride from benzene originate from John M. Weiss and Charles R. Downs in 1918. The oxidation of benzene remains a feasible route to maleic anhydride even today, although since around 1975, n-butane and n-butylene have increasingly replaced benzene as raw materials. n-Butane and n-butylene are available as co-products in steam cracking of naphtha and from natural gas condensates. 

Aldehydes, acetic and formic acids, coming more particularly from steam cracking or even FCC condensates. 

The specific raw material used in cracking processes depends on the natural resources from each geographic region, and this determines the final distribution of olefins.Thus, in Europe and Asia, ethylene is produced from naphtha, gas oil, and natural gas condensates (co-producing propylene, C4-olefins and aromatic compoimds), whereas in the US, Canada, and the Middle East, steam cracking of ethane and propane is mainly employed. One aspect to be considered is the fact that for the production of 1 ton of ethylene in a typical naphtha cracker, 3.3 tons of naphtha are required," while when using ethane only 1.7 tons of feed are needed. 

Furnace carbon black is produced from the incomplete combustion of what is called carbon black oil feedstock, which consists of heavy aromatic residue oils. In the United States this oil is commonly the bottoms from catalytic cracker units. They are commonly referred to as cat cracker bottoms and contain relatively low hydrogen content (and conversely high carbon content). In Europe and other locations, the carbon black oil used is commonly a byproduct of high-temperature steam cracking of such products as naphtha, gas condensate, and gas oil to produce ethylene, propylene, and other olefins. Here, no catalysts are used in the cracking process. These types of carbon black oils are mainly unsaturated hydrocarbons. A third source of carbon black feedstock is coal tar, which is commonly used in China to manufacture carbon black. 

If inert material is to be added, then ease of separation is an important consideration. For example, steam is added as an inert to hydrocarbon cracking reactions and is an attractive material in this respect because it is easily separated from the hydrocarbon components by condensation. If the reaction does not involve any change in the number of moles, inert material has no effect on equilibrium conversion. 

Naphtha desulfurization is conducted in the vapor phase as described for natural gas. Raw naphtha is preheated and vaporized in a separate furnace. If the sulfur content of the naphtha is very high, after Co—Mo hydrotreating, the naphtha is condensed, H2S is stripped out, and the residual H2S is adsorbed on ZnO. The primary reformer operates at conditions similar to those used with natural gas feed. The nickel catalyst, however, requires a promoter such as potassium in order to avoid carbon deposition at the practical levels of steam-to-carbon ratios of 3.5—5.0. Deposition of carbon from hydrocarbons cracking on the particles of the catalyst reduces the activity of the catalyst for the reforming and results in local uneven heating of the reformer tubes because the firing heat is not removed by the reforming reaction. 

Steam condensed in a thin film along the cold tube surface. This thin film of condensate then dissolved ammonia and oxygen present in the steam, which, in combination with stress, produced the observed cracking. 

Vacuum Distillation - Heavier fractions from the atmospheric distillation unit that cannot be distilled without cracking under its pressure and temperature conditions are vacuum distilled. Vacuum distillation is simply the distillation of petroleum fractions at a very low pressure (0.2 to 0.7 psia) to increase volatilization and separation. In most systems, the vacuum inside the fractionator is maintained with steam ejectors and vacuum pumps, barometric condensers, or surface condensers. 

Cracking imposes an additional penalty in a vacuum unit in that it forms gas which cannot be condensed at the low pressures employed. This gas must be vented by compressing it to atmospheric pressure. This is accomplished by means of steam jet ejectors. Ideally, it would be possible to operate a vacuum pipe still without ejectors, with the overhead vapors composed only of steam. In practice, however, leakage of air into the system and the minor cracking which occurs make it necessary to provide a means of removing non-condensibles from the system. In addition to the distillation of atmospheric residuum, the lube vacuum pipe still is also used for rerunning of off specification lube distillates. 

Cracking imposes an additional penalty in a vacuum unit in that it forms gas which carmot be condensed at the low pressures employed. This gas must be vented by compressing it to atmospheric pressure. This is accomplished by means of steam jet ejectors. 

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