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Tue 23 Feb 2010 04:00 AM

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Flow control

Due to the importance of valves at any petrochemicals plant, buyers should make sure all aspects are covered before making a final decision.

Due to the importance of valves at any petrochemicals plant, buyers should make sure all aspects are covered before making a final decision.

In an industry where the smallest leakages could cause a disaster, flow control plays a critical role in safeguarding plants from disaster and in maximising production of the different products. Key to this process is valves.

The first step in the production of petrochemical is cracking the feedstock, whether ethane or any other heavier feed like naphtha, into ethylene and propylene.

This cracking process take place in a furnace, and it is called pyrolysis which is the thermal cracking of petroleum hydrocarbons with steam, also called steam cracking. "Valves in the furnace section play a critical role in maximising ethylene production and throughput," says Ian Turner, general manager of IMTEX Controls.

"There are three critical control valve applications in the furnace area including dilution steam ratio control, feed gas control, and fuel gas control," he explains.

Precise control of the steam dilution valve is necessary to maintain the proper steam ratio, which can greatly affect the efficiency of the furnace, while the feed gas control valve controls the flow of feedstock used in the ethylene plant. Tight control of the valve is critical in the steam dilution valve so that the proper reaction ratio can be maintained within the furnace, and thus avoids wastage.

Fuel gas regulates the temperature of the furnace by controlling the fuel to the burners. "Due to the nature of the fuel, many plants use emissions control packing to limit the emissions of the fuel gas. This is for environmental concerns as well as general safety reasons," says Turner.

"As with the other valves in the furnace area, due to location, the fuel gas valve may also see high ambient temperatures. Depending upon on the ambient temperatures for each particular application, special care may need to be taken in selecting the actuator and accessories," Turner explains.

Buyer's Guide

Purchase managers should look at various aspects before taking the decision on which valve should be used in their plants. "Operational effectiveness in today's plants is critical.

Today's Fisher Control valves are high performance engineered solutions designed to achieve this goal 100%," says Jose Mathew, sales director, Middle East and Africa, Fisher Valve Division at Emerson Process Management. "Reliability of the control valve assembly is a key in achieving a high standard of operational effectiveness," Mathew adds."The buyer of control valves today is looking for a reputable supplier with the technology to support the products, and it also has the necessary local support and expertise to meet their plant needs over the life cycle," says Christophe Melinette, managing director Tyco Flow Control Middle East. "The supplier should have all the necessary international type of approvals, industry standards and quality certification to back up his products," he adds.

There are a broad range of valve specifications and standards in use today. These include international standards and regulations as well as customer specifications. "Valves specifications are determined by the end user and the engineering contracting houses that design and build the plants," reveals Melinette.

Common standards are developed by international agencies. "These standards are in-depth and highly diverse, while customer standards are often dependant on the criticality of the application in the process or other customer needs. A control valve supplier should be able to provide a broad array of products, services, and test capabilities to comply with these needs," explains Mathew.

Not a Commodity

Whether it is a gas feedstock or a liquid, each process has a unique set of operating pressures, temperatures, flow rates, material requirements, and many others specific parameters or requirements.  The type and configuration of a control valve is dependant on all of these.  Therefore, it is very difficult to identify an average price of a valve for a plant as it is also dependent upon what the plant is manufacturing and the size of the plant.

Today's control valves come in multiple configurations, sizes, and types. "They can generally range from under 1 inch in size to over 72 inches in size. Materials can be simple carbon steel to exotic high nickel alloys, as you would expect the price of the control valve is highly dependent on these factors.

A common control valve can range from around $1000 to over $250 000,"says Mathew. Control valves are truly a long term investment for a customer and their operation, not a commodity.

Though the prices of these valves can't be determined easily, demand from petrochemicals producers in the Middle East can be noticed easily giving the fact of the huge downstream projects launched in the region.

"There is strong demand within the region for petrochemicals. In the past there has been a great deal of investment in new plants in and around the Gulf Region," says Melinette. "Looking at investor reports and independent surveys there are also future investments waiting for the green light to proceed," he concludes.

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