XV Международная студенческая научная конференция Студенческий научный форум - 2023

The control valve is the main element of the control circuit. Usually it transforms from 1 to 5 kilowatts of thermal power (the average pump power in chemical plants) and even more. For example, in the petrochemical industry – from 5 to 200,000 kilowatts of thermal power, which is a typical range of capacities for high-efficiency pumps and machines for continuous technological production or the total capacity of the entire plant, which is blocked by shut-off or control valves. In the oil and gas industry, many types of valves are powerful power converters (inverters). From an economic point of view, these fittings often work more or less successfully under high stress loads, which is characterized by additional costs for reducing the noise level of products, maintenance, or if serious problems occur, it can even lead to a production shutdown, i.e. low or high operating costs.

End-users, owners of petrochemical plants, often request the following priorities concerning valves: safety and reliability, quality of regulation, aspects of environmental protection, uninterrupted operation, the lowest operating costs on the part of the owner. The customer also has claims to the cost of maintenance and the number of necessary spare parts, which are the most significant of the after-sales costs. There are some factors that make it difficult for the valve manufacturer to meet the customer's requirements, for example: due to the double effects of corrosion and contamination of the working environment, the valve body and its internal parts are subject to wear. Cavitation and boiling in combination with the impact of the output velocity of a pure liquid or steam-water mixture from the valve can lead to serious problems, the worst of which may be the shutdown of production [2].

Often at the initial stage of planning, electronic bidding and when choosing a control valve, time is the most important factor. Unfortunately, this leads to the fact that the choice of reinforcement occurs with huge losses due to the fact that the detailed design of the reinforcement is not taken into account. Although at the same time, all technical responsibility falls on the manufacturer of the valve.

The purpose of the research: to review the problems of the functioning of control valves in severe operating conditions of petrochemical industries, to identify the optimal design of valves and offer solutions for their optimization.

Materials and methods of research

The study was conducted on the basis of information from the Internet. The work of petrochemical enterprises was analyzed, as well as reviews and comments from manufacturers of pipeline fittings were considered.

Research results and their discussion

Typical for urgent projects is the fact that in order to avoid fines, it should be taken into account that some control valves may fail even at the start-up stage of large production facilities. And this is despite the fact that during the traditional commissioning process, their uninterrupted operation is guaranteed with the replacement, if necessary, of critical fittings along with fittings and pre-purging of the entire system. If planning errors are discovered for the first time at this stage, a huge number of difficulties can affect the success of the project, due to the fact that the calculations of the technological conditions of the project were inaccurate, or the choice of control valves was hasty and illegible. At the same time, the following questions arise: "Who is responsible for the safety of the plant?" and "Is the process of electronic trading (bidding and buying) of heavy-duty control valves or other special valves too fast?" A shorter decision time associated with anonymous bidding may mean that key characteristics and tasks, such as plant safety, quality control and long-term operation, may be missed.

From the point of view of the valve manufacturer, this situation is difficult due to the fact that both aspects of competitiveness and reliability should be fulfilled. Many trademarks of well-known companies and the fittings they produce disappear or are absorbed by other larger firms. This is how huge conglomerates arise. The process of "efficiency of joint efforts" continues more or less successfully. It should be understood that the chronicle of factory disasters will never stop. But it is impossible to allow an increase in risk due to the fact that fittings designed for difficult operating conditions (high pressures and temperatures) are calibrated and selected "quickly and indiscriminately", without detailed study, which requires time. The question arises: is it possible to find an optimal way that would meet the requirements of both the present and the future [4]?

In recent decades, hydrocarbon processing facilities, including oil refineries, methanol production plants, liquid natural gas storage facilities and transportation systems have increasingly increased in size to ensure high productivity. Engineers and designers solved the difficult task of finding new economic solutions. Their goal is to reuse raw materials and save energy consumption in order to meet the increasingly stringent requirements of environmental legislation. Further goals are to significantly reduce the level of both internal and external valve leaks, reduce noise from the operation of control valves, as well as operating costs and the costs of an unforeseen shutdown of production. This causes the need for large-diameter control valves, which should have the lowest level of leaks in the seat, as well as not have increased sensitivity to dust.

From the experience gained as a result of the increased number of identified malfunctions at petrochemical and oil refineries over the past time, the following conclusion can be drawn: it is important to make sure that modern, low-weight designs of shut-off valves and rotary type valves are selected in strict accordance with their limited range of applications. More recently, only valves for heavy-duty applications with high performance characteristics - cell-type shut-off valves (Fig. 1) or with a control element mounted on top or bottom – could correspond to the entire range of applications [5]. For less harsh operating conditions, this valve was designed anew.

Fig. 1. - Diagram of the cell valve design

Traditional cellular balanced shut-off valves function correctly if the working fluid does not contain any contaminants or solid particles and if unstable temperature and pipeline voltage do not attack the perfect design tolerance system. But with large valve passes, this can lead to extremely high initial and operating costs. Malfunctions such as a low level of regulation due to increasing friction parameters, as well as jamming and blocking of valves may occur if mud filters, condensate drains, corrective forces on the device pipeline are not installed or are not functioning properly. Maintenance can become an important expense item.

The requirement to reduce costs meant that this generation of fittings was replaced in simpler operating conditions by inexpensive, lower-weight fittings. Rotary disc valves with low or higher performance characteristics, as well as other non-rotary type fittings have been developed for individual market segments.

Rotary type plug valves are economically advantageous when they replace shut-off valves, but there is a risk that engineering competence will not be sufficient to apply them to critical operating conditions. Before releasing any product to the market, it is necessary to spend both time and effort on testing new reinforcement designs on test benches. The lack of operational data due to the limited capabilities of test benches is often compensated by the practice of troubleshooting or trial and error. Typical valve characteristics are given in international standards, such as the standard of the International Electrotechnical Commission "EN IEC 60534". Individual measurements of actual valve factors or their approximate data are stored in the proprietary software of competent valve companies.

Most of the potential problems can be predicted using modern software, provided that the operating limits are known, and the valve manufacturers have reported the specific characteristics of the load on the valve: Cv, xFz, Fl, xT and Fd. For example, the CONVAL-6 software is suitable for the measurement parameters of both the entire enterprise and the fittings. Dynamic diagrams are compiled using the established characteristics concerning flow, power, speed increase and output speed as the value of the Cv throughput coefficient and the valve stroke. The program is an independent optimization tool for the manufacturer of fittings and pipeline parts, which includes data on materials and properties of more than 1000 substances, including hydrocarbon. Ethylene, propylene, chlorine, natural gas

Warning indicators can be used to indicate a point in the selected valve system on the pipeline where mechanical overload may occur due to high speeds or where the noise level does not meet the established requirements (Fig. 2). It should be noted that too high speeds of moving parts of the valve at the valve outlet are the main causes of malfunctions in the valve, especially when it is used to control corrosive media.

Fig. 2. Modeling of the valve body and analysis of its hazardous areas

The software provides the user with new calculation methods, including the graphical part. This makes it easier to control the operation of the control valves, and also provides a new most cost-effective solution for noise reduction. The use of modern engineering modeling systems makes it possible to avoid design errors at the first stages, as well as to select and perform calculations of optimal housing materials. These systems increase the accuracy of engineering work, minimize the chance of error, which allows us to reach a higher level of production, which is so often required by customers at oil and gas facilities.

Depending on the design features and applications, there are different solutions to the problems of how to avoid critical noise levels and mechanical malfunctions in the operation of the valve (for example, the use of an anti-cavitation headset):

- the "V-port trim" design for the internal parts of pipe valves of general use, characterized by strict limitation of output speeds and other operating parameters;

flow dividers;

noise reduction devices on the downstream pipeline for the descent of gas and steam under pressure;

perforated plunger (fig. 3);

- multi-stage maze design.

Fig. 3. Perforated valve plunger

If the sound pressure level (SPL) of the V-shaped design of the internal parts of the control valve is not suitable for this liquid or there is a need to avoid cavitation and corrosion, it is recommended to use a unique design of the valve with a balanced gate (AC Trim System), which is resistant to vibration and contamination. The maximum pressure drop of 25 – 40 bar depends on the properties of the working fluid [3]. Table 1 shows the advantages and disadvantages of various designs of the internal device of the valve:

Table 1

Various designs of internal fittings, their advantages and disadvantages for severe operating conditions

Type of shut-off valve	Xfz, for 75% valve load	Xfz, for  75% valve load	Стойкость к загрязнению	Стойкость к вибрации
Cellular, with a balanced piston	0.25  0.35	until 0.5	low	high
Parabolic shutter	0.25  0.35	until 0.8	high	low
Shutter with V-shaped entrance	0.25  0.35	until 0.5	high	high
Perforated shutter	0.25  0.35	0.25  0.35	low	high
Balanced Shutter (AC Trim System)	0.35  0.5	until 0.85	high	high

Conclusions

In the course of the analysis of the available information, the problematic aspects in the use of regulating pipeline fittings at petrochemical industry facilities were considered; physical processes arising from the movement of various types of liquids were described; difficulties and problems that arise when solving commercial issues and neglecting technical analysis were described; optimal valve designs and methods for reducing cavitation noise were proposed.

References

Baumann H. Control Valve Primer. – Chapter Saving Energy – ISBN 1-55617-323-7.

Neftegaz.ru. Science and technology // Transportation and storage. [electronic resource]. URL: https://clck.ru/337rcv. (date of application: 12.12.2022)

Samson. Pipe fittings // Single-seat and cellular valves. [electronic resource]. URL: https://clck.ru/337rfx. (accessed: 12/21/2022)

4. "ADL". Development, production and supply of equipment for engineering systems. // Rules for the selection of control valves. [electronic resource]. URL: https://clck.ru/337rmu. (accessed: 12/22/2022)

«TrubyPro.ru. Website about pipes". Valves // Varieties of control valves. [electronic resource]. URL: https://trubypro.ru/dopolnitelnye-elementy/klapany/reguliruyushie.html

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