## 2 Materials and Methods
Gases in the state of steam from the top of the stripping column C-1 come out with a temperature of 135 \({}^{\circ}\)C, then they pass through the chiller-condensers XB-101 and XK-1 and with a temperature of 35-40 \({}^{\circ}\)C enter the separator S-2. From this separator S-2, the liquid phase is returned to the stripper C-1. The settled water in the S-2 separator is discharged into the sewer. Hydrocarbon gas from the S-2 separator for hydrogen sulfide removal enters absorber C-3, and hydrocarbon gas from the top of absorber C-3 is fed to the fractionating absorber C-6 of the reformer or the refinery's fuel network. Thus, in the process of hydrotreating, a chemical transformation of a substance occurs under the influence of hydrogen gas with high pressure and high temperature. In the process of hydrotreating, sulfur compounds are reduced in the composition of petroleum products, fuels, a saturation of additional unsaturated hydrocarbons occurs, the composition of tar, oxygenated compounds decreases, as well as hydroracking of hydrocarbon molecules. Improving refinery hydrotreating processes using modeling methods allows [24]:  
* to carry out hydrotreating processes in the optimal mode, which maximizes the productivity of the facility and the yield of target products;
* to improve quality indicators of manufactured products. This paper proposes an effective approach to the development of mathematical models and modeling of technological objects on the example of units of the hydrotreating block of the Atryau refinery. A number of research works are known on methods of mathematical modeling and optimization of technological objects and oil refining processes, including the process of hydrotreating, for example [25; 26]. However, in practice, production situations can often arise associated with a shortage and indistinctness of initial information, problems of modeling and optimization of their operating modes, the formulation and solution of which using traditional methods do not provide adequate solutions. Such objects include the hydrotreating unit of the LG unit at the Atryau refinery, the main units of which operate under conditions of uncertainty associated with randomness and with indistinctness of initial information [27]. In this regard, it will be necessary to develop mathematical models of the main hydrotreating unit the Atryau refinery on the basis of a systematic approach, i.e., using available information of various nature. Development of Mathematical Models of Technological Objects Functioning in Conditions of Indistinctness of Initial Information  
To develop methods for constructing models of technological objects, which are characterized by the fuzzy initial information, we use the methodology for modeling complex objects in conditions of uncertainty and a hybrid approach to the development of mathematical models, proposed by us elsewhere [27; 28]. Of the various approaches to developing models based on fuzzy information, three can be distinguished:  
1. an approach based on the idea of regression analysis, taking into account the fuzziness of some part of the initial information;2. an approach based on the use of logical rules for conditional inference, used in the conditions of fuzzy input and output parameters of the object;
3. combined approaches. We turn to the study and description of the first approach based on the use of regression analysis taking into account fuzzy information. Using this approach, the structure of the models is identified in the form of regression models with fuzzy coefficients. Fuzzy models built on the basis of this approach are successfully used in modeling and control of a number of chemical-technological systems of oil refining [3,4,27] and can be used to model objects in other industries.