A system method is proposed, which allows to develop a package of models of interconnected technological units of chemical-technological systems using various available information. On the basis of this method the system of models of the main interconnected units of hydrotreating unit is developed. The problem of decision making in fuzzy environment has been formulated for controlling the hydrotreating process in fuzzy environment based on the developed system of models applying the Pareto optimality principle for fuzziness. A heuristic method of solving the problem of decision making for controlling the hydrotreating process in fuzzy environment has been formulated. The novelty of the proposed heuristic method lies in the maximum use of initial fuzzy information, in the form of experience, knowledge of experts, which provides high adequacy of the decisions made in a fuzzy environment. The obtained results have been applied in practice to solve decision-making problems for control of hydrotreating process at Atyrau refinery. The advantages of the proposed fuzzy approach to solving the decision-making problems of hydrotreating process control by known methods have been shown.

High-quality motor gasoline is produced at refineries worldwide using hydrotreating processes in the presence of catalysts [1-4]. Currently due to the growing demand for high-quality motor fuels that meet the increasingly restrictive environmental requirements, effective management of hydrotreatment of gasoline fractions and production of high-quality motor gasoline has become an urgent task for refineries. All Kazakhstani refineries use process catalytic reforming and cracking units for thermocatalytic processes, which were studied in work [5].

Catalytic reforming units are designed for reforming straight-run gasoline fractions from primary oil refining units with the purpose of producing high-quality gasoline and aromatic hydrocarbons in the presence of hydrogen and catalyst [6, 7]. Whereas catalytic cracking units are designed to decompose heavy low-value petroleum products (fuel oil, tar sands, solar oil, etc.) into more valuable products (petrol, gasoline, raw materials for petrochemicals, etc.) in the presence of a catalyst. In these units at high temperatures the heavy hydrocarbon molecules are split and broken down into lighter molecules as they pass through the catalyst. Catalytic cracking processes, in which destructive transformation of various oil fractions into motor fuels and raw materials for petrochemicals takes place, have been studied in works [8, 9].

In the processes of petroleum and petroleum products refining, which contain sulfur-, oxygen- and nitrogen-containing compounds that negatively affect the further stages of refining, an important role is played by hydrotreating processes designed to purify raw materials from sulfur and other harmful organic compounds in the presence of a catalyst. Gasoline fractions are hydrotreated to remove hetero-organic compounds of sulfur, nitrogen, oxygen, arsenic, halogens, metals and hydrogenation of alkenes, which allows to improve the performance and quality of motor fuels. Thus the hydrotreating process allows to reduce corrosive aggressiveness of motor fuels and their tendency to form precipitates, to ensure compliance with environmental requirements for fuels by reducing the amount of toxic gas emissions into the environment.

The chemistry and technology of hydrotreating of fuels are investigated in work [10]. The work [11] is dedicated to the study of hydrotreating processes of straight-run gasoline fractions on ball alumino-nickel-molybdenum catalysts. Since hydrotreating process is one of the most important and widespread processes in refineries the issues of hydrotreating units operation mode control on the basis of their models are given special attention. Such problems are often efficiently and promptly solved in practice on the basis of decision-making methods, which allow searching and determining the optimal parameters of hydrotreating process. And optimal parameters, in their turn, ensure effective operating modes of units, in which hydrotreating processes take place when maximum volumes of target products are obtained and quality thereof is improved.

A large number of research works are dedicated to the problems of control of chemical technological processes (CTP) and systems (CTS). Various approaches to the control of technological processes and objects under deterministic conditions on the basis of traditional control methods have been proposed [12-17]. But the problems of decision making on control of CTS operation modes under conditions of multicriteria, contradicting nature and fuzziness thereof on the basis of the system of CTS models have not been completely considered yet in research works. Under these conditions there are known approaches based on transforming the original fuzzy problem to a set of crisp problems by means of α level set [18-20]. However, this approach leads to the loss of a part, sometimes an important part of the collected fuzzy information representing the knowledge, experience and intuition of the decision maker (DM), subject matter experts. In fact, this approach considers fuzzy information only on some points obtained by α slices, whereas the rest of the information is not considered, which in turn reduces the adequacy of the solution.

To effectively solve and obtain a more adequate solution of fuzzy decision-making problems of technological processes management a system approach based on the mathematical apparatus of fuzzy mathematics should be applied [21-23]. The system approach using fuzzy information allows to develop a package of interrelated CTS models, on the basis of which it is possible to make an adequate decision on the management of technological processes occurring in fuzzy described CTS. Such decision-making methods for fuzzy control allow to take into account experience, knowledge and intuitions, i.e. intelligence of DM, subject matter experts, which is expressed in verbal form (judgments, conclusions in natural language).

When formalizing and solving the problems of fuzzy control of technological processes it is necessary to use the collected and available fuzzy information to the maximum extent possible, i.e. it is necessary to apply heuristic approach based on the creative ability of DM, experts. In this regard the proposed work dedicated to the development of a package of models of hydrotreating unit of catalytic reforming unit and an effective method of decision making for hydrotreating process control on the basis of heuristics, is a relevant task of the theory and practice of modeling and control of technological processes under the conditions of deficiency and fuzziness of initial information.

The purpose of the research work is to develop a package of models of hydrotreating unit and heuristic decision-making method for fuzzy control of hydrotreating process under the conditions of deficit and fuzziness of initial information.

In order to achieve the formulated goal the following research objectives are set and solved:

- to investigate the influence of the main technological parameters of the hydrotreating unit on the hydrotreating process;

- to develop a package of models of the main units of hydrotreating unit of catalytic reforming unit LG-35-11/300-95 on the basis of available information of different nature;

- to formulate a mathematical formulation of the decision-making problem for controlling the hydrotreating process in a fuzzy medium on the basis of models of the main units of the hydrotreating unit and to develop a heuristic method for solving thereof.