An important component of today's global community is the continuous competition of the leading countries in the energy market. Conventional oil and natural gas are dominating in the economies of the developed and developing countries. Hydrocarbons and their products directly affect the geopolitical processes in the world and are connected with such processes, acting as a guarantee of energy security of countries on the one hand, and powerful arguments in the foreign policy arena on the other hand.
But these resources are exhaustible or inaccessible to many countries for various reasons, and in this regard in recent decades there has been great interest to the industrial production of hydrocarbons from syngas.
The process for producing hydrocarbons from syngas is based on research by German chemists F. Fischer and H. Tropsch in the 1920s, and the process itself is widely known as the “Fischer-Tropsch reaction”. To date, the most known three types of processes for producing liquid synthetic hydrocarbons depending on the type of feedstock for syngas production are as follows:
- GTL (Gas to liquids) - here the raw material is gas (natural gas, associated gas, or shale gas);
- CTL (Coal to liquids) - here the raw material is coal and other combustibles;
- BTL (Biomass to liquids) - biological raw materials and waste are used as the raw material.
CTL process is the most widespread due to the fact that, for example, proven reserves of lignite are several times greater in energy equivalent vs. the reserves of oil and natural gas combined.
The largest CTL plants are located in South Africa, which since 1955 (being unable to import oil and petroleum products) has had to make up for the shortage of these by setting up production of liquid synthetic hydrocarbons from inexpensive coal mined at local deposits. And nowadays the most ambitious projects are being implemented in China, which is actively building and commissioning liquid synthetic hydrocarbons production plants.
Of course, implementing the process of liquid synthetic hydrocarbons production requires taking into account certain nuances, such as environmental safety of the production and fluctuations in oil prices in the world market. But also there are obvious advantages, one of the main is the absence of sulfur and nitrogen compounds in liquid synthetic hydrocarbons, the prospects of using the latter as a finished product or as an environmentally friendly raw material in the chemical and petrochemical industry.
Global SO in cooperation with the leading applied institutes of Russia has developed a Conceptual design of a pilot plant for the production of liquid synthetic hydrocarbons using CTL process. The way of processing coal into liquid synthetic hydrocarbons includes the following stages: fuel preparation, gas generation, gas treatment, adsorption of sulfur compounds, steam conversion of generator gas, carbon dioxide absorption, Fischer-Tropsch synthesis, and steam-carbonic acid conversion of purge gas. Water steam, oxygen, and electricity are used to make the process running. And it is possible to obtain electricity for the balance-of-plant needs in the process cycle.
Catalytic synthesis of hydrocarbons is performed in an adiabatic Fischer-Tropsch reactor of shell-and-tube or spiral type using a cobalt catalyst and recirculation of the gas flow. The synthesis produces C1...C4 (gases) light hydrocarbons, C5...C12 (gasoline fractions) medium hydrocarbons, and C13...C18 (diesel fractions) heavy hydrocarbons. Diesel fractions account for the bulk (up to 80%).
The target marketable products are separately produced diesel fractions (80% of liquid synthetic hydrocarbons yield) and gasoline fractions (20% of liquid synthetic hydrocarbons yield).
Additional target marketable products are separately produced heavy resins (80% of the resin yield) and light resins (20% of the resin yield).
Marketable by-products are liquid carbon dioxide, and liquefied sulfur dioxide.
Production waste: coal chips, coal dust, slag, waste water, carbon dioxide emissions (reduced by 30 times as compared to direct coal combustion due to liquefaction and use of carbon dioxide in the process itself), sulfur compounds emissions (reduced by 1,000,000 times as compared to direct coal combustion due to deep treatment of generator gas from sulfur compounds and capture and liquefaction of sulfurous gas), nitrogen oxides emissions (reduced by 1,000 times as compared to direct coal combustion due to using oxygen-steam blast).
Features in Brief
- oxygen-steam blast during coal gasification making it possible to significantly reduce capital expenditures for the key process equipment by reducing its specific amount of metal per structure;
- original design of the forge gas generator making it possible to increase specific load on the operating volume by using special gas lances and augers;
- two-stage desulfurization, providing a residual content of sulfur compounds in the synthesis at a level below 0.6 ppm;
- a unique natural adsorbent of sulfur compounds, which has a large sorption capacity;
- preventing the discharge of sulfur compounds into the environment by collecting and liquefying sulfurous gas;
- sharp decrease of carbon dioxide discharges into the environment due to its liquefaction and use in the process of steam-carbonic acid conversion of purge gas;
- separation of anhydrous coal tar in the technological process for subsequent sale as an additional target marketable product;
- original formula of cobalt Fischer-Tropsch synthesis catalyst providing high level of carbon conversion, high selectivity for liquid synthetic hydrocarbons and allowing to significantly reduce the required amount of catalyst per unit of liquid synthetic hydrocarbons yield;
- original design of Fischer-Tropsch synthesis reactor, which makes it possible to provide a specified thermal regime and a high yield of liquid synthetic hydrocarbons;
- original Fischer-Tropsch synthesis process arrangement, which makes it possible to obtain the key target product - diesel fractions - in water-free form without an additional separation unit;
- a highly efficient device for separating water condensate and gasoline fractions using physical processing methods to obtain gasoline fractions as the main target product;
- highly efficient device for separation of water condensate and gasoline fractions using physical processing methods to obtain gasoline fractions as the key target product;
- steam-carbonic acid conversion of purge gas, which makes it possible to obtain an additional amount of the target product, liquid synthetic hydrocarbons;
- high specific yield of the target product, gasoline and diesel fractions;
- possibility of selling liquefied sulfur dioxide gas as a marketable by-product;
- possibility of obtaining liquefied carbon dioxide as a marketable by-product;
- maximum use of thermal resources released in the process.