Technology
Details of Dynacracklng process revealed Hydrocarbon Research process for upgrading crude
Dynacracking reactor has three processing zones
oils uses fluidized-bed reactor and can produce distillates
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and naphtha or fuel gases
Escalating crude oil prices have placed new emphasis on processing of the crude to maximize high-value products. One contender in the crude upgrading competition, Hydrocarbon Research Inc., has been reviving its Dynacracking process as its prime entry (C&EN, April 7, page 5) and has recently revealed some details of the reactor and presented some new economic data. Dynacracking originally was developed in the 1950's but was shelved because a heavy crude oil process wasn't economically viable at the time. But when the company revived Dynacracking, the experience it had accumulated was already enough for it to consider an immediate scaleup to commercial size. To that end, a three-phase plan was initiated in April 1978. This provided the preliminary engineering data. A year later five client companies sponsored a basic engineering design package for a 5100 bbl-per-streamday unit to process vacuum residue. This work has now been finished, and engineers are currently moving into a detailed design, engineering, procurement, and construction phase. If all goes as planned, the first commercial scale Dynacracking plant will be operating in 1982, about 30 years after the process was first proposed. Dynacracking can be operated in several modes, depending on the degree of severity imposed. In general, the low-severity modes favor distillates and naphtha, and high-severity modes favor production of synthetic fuel gases. Because the process is noncatalytic, it can handle a great variety of feeds with no fouling of catalyst by either sulfur or heavy metals. Considerable desulfurization is obtained in all modes of operation. The heart of the process is a unique fluid-bed reactor divided into three 24
C&EN July 28, 1980
••Products
Hydrocracking zone
Stripping zone (packed section)
Gasification zone
M
-Feed
UL
II τ
-Recycle
Regenerated particle riser Steam and oxygen
Steam or gas
zones separated by internal baffling. Fresh feed, with or without distillate recycle, enters the lower part of the top zone. This is the hydrocracking zone and is maintained, at tempera tures from 900° to 1400° F. Products include gaseous hydrocarbons, naphtha, distillate, and coke. The coke and some very heavy liq uids are deposited on the inert parti cles that form the bed. These heavier particles fall through a stripping zone in the central part of the reactor. This zone is filled with inert, stationary packing that separates the lower and upper parts of the fluid bed and strips the heavy liquids from the falling particles. In the bottom section (gasification zone), the coked particles are con tacted with steam and oxygen at temperatures up to 1800° F to gasify the coke. This yields a synthesis gas that forms the stripping medium for the stripping zone above and is the nominal fluidizing medium for all sections of the tower. Except for startup, no external heat source is necessary to operate the plant. The partial pressure of hydrogen in the hydrocracking zone is high enough to provide several advantages, according to Hydrocarbon Research.
It reduces the coke and olefin yield, provides for a greater liquids yield, and ensures a high naphtha yield. The total reactor pressure ranges from 400 to 600 psig, and the hydro gen partial pressure never exceeds 175 psig at the feed inlet. There are probably as many ways to operate a Dynacracking plant as there are kinds of crude oil to be upgraded. Upgrading costs can range from $3.09 to $7.98 per bbl for several options cited by the company as typical prospective installations. The case for these data is a 2000 bbl-perstream-day unit, but larger sizes generally yield an economy of scale. Two other cases are cited that em phasize naphtha production in the product slate. For a 5100 bbl-perstream-day unit, return on invest ment is estimated to be 16.7% and for a larger 20,000 bbl-per-stream-day unit 29.7%. G
Project to evaluate natural gas hydrates After a decade of speculation and sometimes polite disinterest by the energy community, natural gas hy drates may be on the verge of finding some recognition as a genuine energy resource. The Gas Research Institute has initiated a two-part project de signed to determine the potential of the hydrates and what they can offer the U.S. in terms of recoverable nat ural gas. Natural gas hydrates, discovered in 1970, are a kind of naturally occurring clathrate, or lattice, in which the host molecules are water and the guest molecules are methane. For practical purposes the solid hydrates can be considered low-pressure forms of ice. More than 170 scf of natural gas, mostly methane, may be contained in 1 cu ft of hydrate, according to Mal colm A. Goodman, president of Enertech & Research Co., Houston, which is involved in the new hydrate project. There has been speculative interest in Arctic distribution of hydrates in connection with gas deposits. The speculation is of more than academic interest because, if there are consid erable quantities of hydrates present,
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C&EN July 28, 1980
Title
the Arctic gas deposits may be much larger than previously estimated. Available pressure-temperature equilibrium data indicate that the Arctic gas deposits are a good bet to obtain the clathrates. The presence of small amounts of propane and/or ethane in the gas would shift the equilibrium in favor of formation of the clathrates. According to Goodman, the hy drates exist both in and below the permafrost zones. These zones are frequently penetrated during ex ploratory and production drilling and can cause troubles from the unusually high intrusion of gas when hydrates are present. So far there has been no systematic exploration for the hy drates and the GRI project is aimed at correcting this deficiency. So far no hydrates have been en countered at Prudhoe Bay, but there is evidence of them from an explora tory gas well to the northwest where the permafrost is 2400 feet deep. The hydrates are expected to be found also in the National Petroleum Re serve. Canadian drillers have found evi dence of hydrates in the Mackenzie Delta, the Arctic islands, and offshore in the Beaufort Sea. All the evidence is somewhat inferential and is based on interpretations of drilling logs. The Soviets claim to be exploiting hydrates in a Siberian gas field, but
experts express some doubt about this. Goodman notes that there is considerable evidence suggesting that the natural gas the Soviets claim to have produced from the hydrates is associated with a free gas zone below the hydrate layer. Two conferences on hydrates have been held in the U.S. The consensus is that hydrates may be a significant energy resource but that there is no real data from which to estimate the economic potential or the technical feasibility of exploiting them. The GRI project is aimed at first assessing the occurrence of hydrates and the technology that would be involved in recovering the gas. If there is a posi tive result, a long-term development plan would then be formulated for the exploitation of the resource. The first part of the project is expected to re quire two years to complete. D
Open-cycle OTEC promises energy, water Looking like a giant mushroom rising above the surface of the ocean, the latest design in ocean thermal energy conversion (OTEC) promises to give distilled water as a by-product of electricity generation. The system was designed by Westinghouse Electric engineer J.
Polyethylene piping system joined with gaskets Workers lower a 20-foot section of Spirolite polyethylene pipe into place during construction of a sewer system at Liberty, Tex.—an installation that the pipe manufacturer says marks the first use of gasketed bell and spigot joints with large-diameter polyethylene pipe. The 18-inch-diameter pipe for the 6000-foot system was made by Spiral Engineered Systems, a division of Gulf Oil's Gulf Plastic Fabricated Products Co. Bryant-Curington Inc., engineers for the city, estimate savings with the sys tem of 3 5 % compared to a system of traditional materials such as clay or concrete, because of the pipe's high strength-to-weight ratio, gasketed joints, and light weight (1/10 that of concrete). The heavy equipment and special bedding required with the traditional materials were greatly reduced. And expensive welding equipment normally used for joining polyethylene pipe was eliminated. The pipe is manufactured under an exclusive license for a propri etary German process that makes it possible to produce thermoplastic cyl inders in diameters up to 12 feet.
