Black gold made of coal

The currently high oil prices, which in all likelihood will continue to rise, make the process of liquefaction a very interesting technology for the future. China and South Africa are leading the way and for many other countries with huge coal reserves, coal liquefaction is becoming increasingly cost-effective. Given the current oil prices even the leading industrial nations are finding the process economically attractive. We can therefore expect a global growth in the demand for coal liquefaction. Besides economic factors, it is above all the draw of being independent of imported oil that plays a major role in energy policy. Coal is a fossil fuel that in the course of millions of years has evolved from dead plants, cut off from air and under the pres-sure of layers of rock lying on top. Engineers have been changing coal into oil for a long time now without any problems. In order to generate liquid products from coal ranging from petrol to heavy oil there are two alternative processes – indirect and direct liquefaction.

By means of the Fischer-Tropsch synthesis, gas is produced with steam from red hot coal, which reacts with catalysts to hydrocarbons (indirect liquefaction). The process is at present only being used in South Africa where 9 million tons of oil products (pet-rol, chemicals) are produced annually at a cost of approx. US$ 25 per barrel.

In 1913 Friedrich Bergius invented the process of direct high-pressure coal hydrogenation, for which he was later awarded the Nobel Prize. It was widely used as the Pott-Broche or IG-Farben process. In the Bergius process finely ground coal is suspended in heavy oil. At a pressure of 200 to 300 bar, hydrogen is allowed to react at 500 °C. The whole process and the desired end product can be exactly controlled by various parameters such as sojourn time in the reactor, temperature and catalyst addition. The first industrial plant in the world for direct coal hydrogenation is currently under construction in Mongolia. In the first development stage it will turn out 0.9 million tons of pet-rol, kerosene, diesel and other fuels from 2.1 million tons of coal annually. Within four years these figures will be multiplied by five. Key technological components of this plant are the high-pressure plunger pumps from Uraca.

The demands on the high-pres-sure plunger pump units for handling coal slurry in coal liquefaction are enormous. The pumps not only have to withstand high temperatures and pressures but they also have to cope with the high content of solids and the abrasive properties of the medium. At the same time the pumps operate continuously for this application and the users demand a high degree of availability and operating safety as well as low operating costs in order to make the process profitable. To meet these demands as well as possible Uraca has developed a special pump in the P5-96 series together with auxiliary equipment and back-up units.

The handling medium is coal slurry, consisting of 50 % carrier oil and 50 % finely ground coal. The handling temperature is 290 °C at a pressure of 210 bar.

Owing to the specific peripheral conditions, the challenging handling job requires a pump design that is very different from the technical standard. The special properties of the handling medium, particularly its high solids content and hence abrasiveness and high viscosity, are not only the cause of enormous stress on the pump valves, the whole liquid end and all the parts of the pump that touch the medium are affected. High-strength, temperature-resistant pump materials together with specially integrated cooling and heating equipment ensure smooth thermal expansions. The high-pressure plunger pump has some remarkable design features. For instance, the finely coordinated design of the pump allows it to operate with maximum alignment accuracy in order to compensate thermal expansions of the components. The patented separation chamber ensures that the high-pressure seal does not touch the abrasive solids. In order to withstand the strain, the P5-96 has a crankshaft with six-fold slide bearings. A forcibly coupled injection pump ensures that the packing area is flushed during each suction stroke. All parts of the pump requiring maintenance are easily accessible. The design provides for low wear and tear, meaning long maintenance intervals. An example of this is the particularly large structural shape, enabling low speeds of 30 to 80 min-1 and thus long service life due to low flow speeds in the discharge area. The pump has five plungers and a required power of 95 m³/h. The unit has a total weight of 75 t, the pump itself weighing 38 t.

China is now one of the greatest oil producers in the world, yet due to fast eco-nomic growth it is becoming increasingly dependent on imported oil. On the other hand, China has coal reserves of over 1,000 billion tons. To meet the growing demand for oil and to ensure the country’s self-sufficiency, coal liquefaction provides a cost-effective alternative. Moves in this direction are also necessary for China because the growing motorization of the country will increase the country’s daily demand for oil for road vehicles from currently one million barrels to almost five by the year 2020 – which is what all the cars in western Europe currently consume. One of the biggest Chinese corporations, based in Beijing, is constructing a production plant for coal liquefaction which is due to start production in 2007. The coal needed for the process is mined in the vicinity of the plant. The goal is to produce 5 million tons of pet-rol, kerosene, diesel and other fuels from 9.7 million tons of coal annually. Due to the favourable conditions, the plant will operate at a profit even if the price for crude oil reaches US$ 20 per barrel. The Department of Energy of the State Commission for Development considers this project, which will cost 2.45 billion euros, to be a major contribution to optimizing China’s energy structure. Further projects of this kind are planned in China. Uraca is building six high-pressure plunger pump units for this plant. The units, each of which will weigh 75 t, will supply the reactors with coal slurry. Uraca is providing all the engineering know-how of the high-pressure pumps as well as its vast experience from other coal slurry projects.

As early as 30 years ago Uraca developed and supplied the pumps for extracting oil from coal for a pilot plant at Bottrop. At that time a time-consuming and costly process, this technology has meanwhile become a profitable way of obtaining oil in times of scarce raw materials and rapidly rising oil and gas prices.

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