Regenerator temperature

The final heater increases the regeneration temperature (- 60° C) to pasteurization temperature (at least 72°C) with hot water. The hot water is 1-2° C above the highest product temperature (73°C). Four to six times as much hot water is circulated compared to the amount of product circulated on the opposite side of the plates. 

Coke on the catalyst is often referred to as delta coke (AC), the coke content of the spent catalyst minus the coke content of the regenerated catalyst. Delta coke directly influences the regenerator temperature and controls the catalyst circulation rate in the FCCU, thereby controlling the ratio of catalyst hydrocarbon feed (cat-to-od ratio, or C/O). The coke yield as a fraction of feed Cpis related to delta coke through the C/O ratio as ... 

Thus decreasing the specific heat of combustion results in an increase in catalyst circulation rate. Because of this relationship to coke yield (eq. 9), the increase in the catalyst circulation rate results in a decrease in regenerator temperature. 

Fig. 4. Coke on regenerated catalyst (CRC) versus regenerator temperature at varying O2 content (30).

To maximize the performance of an FCCU, most units mn at one or more unit constraints. Frequently, one of these constraints is the regenerator temperature, which is set by metallurgical limits for safe operations. Process variables on both the reactor and the regenerator side are thus manipulated to keep the regenerator temperature as close as possible to this regenerator temperature limit. 

The presence of contaminant metals on the equiUbrium catalyst can significantly increase the catalyst coking tendency, which in turn results in an increase in regenerator temperature if all other factors remain unchanged. As one example, if the metals on an FCCU equiUbrium catalyst increased from an equivalent-nickel value of 2000 wt ppm to 3500 wt ppm, the catalyst coke factor would increase 30—50%. If all controllable parameters remained constant, the regenerator temperature would be expected to increase 35—50°C and conversion would drop. 

The metallurgy of the cyclone equipment has in recent years focused primarily on type 304 H stainless steel. The 304 H material is durable and easy to fabricate and repair, withstands the high regenerator temperatures, and is oxidation- and corrosion-resistant. Essentially all internal surfaces of the cyclone that are subject to erosion are protected with a 2 cm layer of erosion-resistant lining. When installed and cured, most refractory linings are highly resistant to erosion. 

The normal regeneration temperature for siUca gel is 175°C. In hydrocarbon service, higher temperatures (225—275°C) are recommended to desorb heavy hydrocarbons, which tend to foul the adsorbent during prolonged use (see Silicon compounds). 

It is possible (with lower initial Led temperature, higher initial loading, or higher regeneration temperature or pressure) for the transition paths to contact the saturated vapor curve in Fig. 16-22 rather than intersect beneath it. For this case, liquid benzene condenses in the Led, and the effluent vapor is saturated during part of regeneration [Friday and LeVan, AIChE]., 30, 679 (1984)]. 

Loss of throughput. The combustion of hydrogen to water produces 3.7 times more heat than the combustion of carbon to carbon dioxide. The increase in the regenerator temperature caused by excess hydrocarbons could exceed the temperature limit of the regenerator internals and force the unit into a reduced feed rate mode of operation. 

Loss of catalyst activity. The higher regenerator temperature combined with the formation of steam in the regenerator reduces catalyst activity by destroying the catalyst s crystalline structure. 

If the regenerator temperature eontinues to rise, additional quantities of steam will be added in the form of water spray by either manual or automatie means—first, through one set of injeetion nozzles in the overhead line, then through another set elsewhere. It may beeome neeessary to add steam to the eyelones in order to maintain 1,300°F to the expander. Spray nozzles in the dilute phase might also be used if the temperature eontinues to rise. 

Any further increase in regenerator temperature will not be coiTccted by steam because the maximum steam rate has already been reached. Therefore, line L represents one condition in a progression of uncorrected temperature rises. 

The absorption process usually occurs at moderate pressure, Ionic bonds tend to achieve an optimum performance near 450 psig, but the process can be used for a wide range of pressures. The molecular sieve bed is regenerated by flowing hot sweet gas through the bed. Typical regeneration temperatures are in the range of 300-400°F. 

The normal regeneration temperature in the still will not regenerate heat-stable salts or oxazolidone-2. Therefore, a reclaimer is usually included to remove these contaminants. A side stream of from 1 to 3% of the MEA circulation is drawn from the bottom of the stripping column, This stream is then heated to boil the water and MEA overhead while the heat-stable salts and oxazolidone-2 are retained in the reclaimer. The reclaimer is periodically shut in and the collected contaminants are cleaned out and removed from the system. However, any MEA bonded to them is also lost. 

Silica gels will shatter in the presence of free water and are chemically attacked by many corrosion inhibitors. The chemical attack permanently destroys the silica gels. The other desiccants are not as sensitive to free water and are not chemically attacked by most corrosion inhibitors. However, unless the regeneration temperature is high enough to desorb the inhibitor, the inhibitor may adhere to the desiccants and possibly cause coking. 

With the advent of combustion promoter, the regeneration temperature could be reduced and still maintain full bum. Thus, intermediate temperature regeneration was developed. Intermediate regeneration is not necessarily stable unless combustion promoter is used to assist in the combustion of CO in the dense phase. Table 1-2 contains a 2 x 3 matrix summarizing various aspects of regeneration. 

The following matrix of regeneration temperatures and operating modes shows the inherent limitations of operating regions. Regeneration is either partial or complete, at low, intermediate, or high tem-... 

In most units, the increase in hydrogen make does not increase coke yield the coke yield in a cat cracker is constant (Chapter 5). The coke yield does not go up because other unit constraints, such as the regenerator temperature and/or wet gas compressor, force the operator to reduce charge or severity. High hydrogen yield also affects the recovery of Cj-H components in the gas plant. Hydrogen works as an inert and changes the liquid-vapor ratio in the absorbers. 

Higher regenerator temperatures (>1,250°F or 677°C) exceed the melting point of vanadium oxides, increasing their mobility. This... 

These metals, when deposited on the E-cat catalyst, increase coke and gas-making tendencies of the catalyst. They cause dehydrogenation reactions, which increase hydrogen production and decrease gasoline yields. Vanadium can also destroy the zeolite activity and thus lead to lower conversion. The deleterious effects of these metals also depend on the regenerator temperature the rate of deactivation of a metal-laden catalyst increases as the regenerator temperature increases. 

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