Thermal cracker

G. S. Fung, P. E. Depalm, and P. Sharma. Pour point depression unit using mild thermal cracker. Patent US 6337011,2(X)2. 

Linear programming Boiler/turbo generator system (11.4) Thermal cracker (14.1) >. i Planning and scheduling (16.1)... 

EXAMPLE 14.1 OPTIMIZATION OF A THERMAL CRACKER VIA LINEAR PROGRAMMING... 

Reactor systems that can be described by a yield matrix are potential candidates for the application of linear programming. In these situations, each reactant is known to produce a certain distribution of products. When multiple reactants are employed, it is desirable to optimize the amounts of each reactant so that the products satisfy flow and demand constraints. Linear programming has become widely adopted in scheduling production in olefin units and catalytic crackers. In this example, we illustrate the use of linear programming to optimize the operation of a thermal cracker sketched in Figure E 14.1. 

Table El4.1 A shows various feeds and the corresponding product distribution for a thermal cracker that produces olefins. The possible feeds include ethane, propane, debutanized natural gasoline (DNG), and gas oil, some of which may be fed simultaneously. Based on plant data, eight products are produced in varying proportions according to the following matrix. The capacity to run gas feeds through the cracker is 200,000 lb/stream hour (total flow based on an average mixture). Ethane uses the equivalent of 1.1 lb of capacity per pound of ethane propane 0.9 lb gas oil 0.9 lb/lb and DNG 1.0.

Example 14.1 Optimization of a Thermal Cracker Via Linear Programming 484... 

Cracking large hydrocarbons usually results in olefins, molecules with double bonds. Thats why the refinery cat crackers and thermal crackers are sources of ethylene and propylene. But the largest source is olefin plants where ethylene and propylene are the primary products of cracking one or more of the following ethane, propane, butane, naphtha, or gas oil. The choice of feedstock depends both on the olefins plant design and the market price of the feeds. 

Crude oils contain a certain amount of combined nitrogen which sometimes breaks down in thermal crackers to form these harmful nitrogen compounds. California, West Texas, and Venezuelan crudes seem to break down this way much more readily than other crudes. Catalytic-cracking units convert the nitrogen compounds in their feed to these polymerization catalyst poisons almost without exception. Other basic materials which have poisoned polymerization catalyst at times are sodium hydroxide and diethanolamine. Both of these materials are used extensively for the removal of hydrogen sulfide from the feed to polymerization units. Catalyst poisons of a basic nature can be removed from the... 

The HYDROCARB coal cracking is an advanced process where natural gas is synthesized from the hydrogenation of the carbon containing raw material. Coal is routed to a thermal cracker where it is decomposed to carbon black as a clean fuel and hydrogen as a byproduct fuel. HYDROCARB represents the possibility of a C02-free fossil-based hydrogen economy. The reaction in the hydropyrolyzer operating on bituminous coal is ... 

In 1934, R. K. Stratford at Jersey s Canadian affiliate (Imperial Oil Co.) discovered that the spent clay used in lube oil treating had catalytic effects. Four thermal crackers were eventually revamped to "Suspensoid Cracking" by adding 2 to 10 pounds of powder/barrel feed in 1940. This catalyst was used in a once through mode and improved the yield selectivities from the thermal cracking process (16). 

Sample No. 22 Residue from Thermal Cracker (Iranian Heavy) Heating Rate fi 10 K/tnin Atmosphere Argon 25 cm /min... 

In Fig. 4-23 the distillation curves of samples from conversion processes are shown. The fully distilled residues from a cat-cracker (sample 20) and from a thermal cracker (sample 22) do not contain any substances separable by distillation, but do contain approximately 40-50 wt% crackable substances. From the visbreaker residues (samples 19 and 21) about 20 wt% may still be separated by vacuum distillation. Obviously the residue of a thermal cracker (sample 18) has undergone only atmospheric distillation. Approximately 5 wt% may still be gained from that sample by atmospheric distillation, and an additional 65 wt% by vacuum distillation. 

Fig. 24 shows the distillation curves of a waxy distillate (sample 23) and the residue from a thermal cracker (sample 22). The residue has been distilled exhaustively. It still contains 50 wt% crackable substances. From the waxy distillate about 50 wt% may still be gained by vacuum distillation. 

Fig. 4-23 Simulated Distillation of Samples from Conversion Processes by TG 750 Sample No. 18 Residue from Thermal Cracker (Arabian Light)...

Sample No. 22 Residue from Thermal Cracker (Iranian Heavy)... 

Sample No. 24 Furfural Extract Sample No. 25 Distillate from Thermal Cracker... 

The residue of a thermal cracker (sample 18) seems to demonstrate losses only by distillation since the peak maxima were found in the temperature range 350-380 °C. Those temperatures are very low for a pyrolysis reaction, whereas the activation energy E = 172 kJ/Mole could represent a substance which is either easily crackable or tough volatile. The residue at 800 °C in thermogravimetry (/ 800 = 5.5 wt%) and the conversion in DSC V = 85.5 %) could result from either type of reaction. In this case it is a disadvantage that the instrument does not permit identification of the products formed. 

The activation energy of sample 18 (residue from a thermal cracker) rises from 171.9 kJ/Mol at normal pressure to 187.2 kJ/Mol at 10 bar pressure. This increase of only 10 % indicates that a pyrolysis reaction occurs even at 1 bar pressure, especially since the peak maximum temperatures hardly shift. Sample 19 (visbreaker residue) does not exhibit a vaporization peak under these conditions. 

Figure 11.19 shows the process flow sheet for a pilot-scale fluidized bed gasifier, capable of processing some 20 kg/h of biomass feed, coupled with a thermal cracker and reformer reactor. The reformer is loaded with fluidizable nickel-based reforming catalyst and fitted with gas analysis ports at its inlet and outlet. The system has been used to evaluate catalyst activity and the decay of hydrocarbon conversion with time from a slip stream sample of the raw fuel gas. In this way, it is possible to quantify the frequently reported phenomenon of commercial catalyst deactivation, sometimes quite rapid, from high activity of fresh samples to lower residual activity brought about by various factors, including the presence of poisons (sulphur, chlorine) and coke formation. 

Feedstock Brega Light Arabian Thermal-cracker tar Heavy Arabian Coal-tar pitch... 

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