The growing acceptance and application of ethanol as a viable alternative to petroleum-based fuels places increasing pressure on processing plants to be more efficient and productive in order to stay competitive. It also puts greater emphasis on maximizing process reliability to safely extend intervals between scheduled maintenance shutdowns. Protection of human health and the environment is another vital concern as the industry burgeons.
 
 There are, in fact, many critical applications within a dry grind corn-to-ethanol processing plant where selecting best-in-class control and automated on/off valve technologies can make an important contribution to valve package performance while maintaining or even improving life-cycle costs for the investment. Perhaps the most important involves valve packages used in conjunction with the molecular sieve, where second stage product is produced. This is also where the most volatile stage of the product is created, so tight shut-off, stem emissions control and safety are important concerns.
 
 In addition, valves leading into and out of this process have high cycles that could result in premature valve failure, seat leakage and significant downtime. Valve leakage in this critical area can make it difficult or impossible to meet product requirements. A single carefully selected valve can answer a large number of concerns.
 
 In addition to precise modulation, control valves used in the molecular sieve process sometimes require a tight bi-directional shut-off to prevent process disturbances. A frequently employed solution is to use two valves: a modulating valve and a block valve for tight shut-off. Another option is to use a special soft-seated control valve designed to provide a tight shut-off, making it possible for a single valve to deliver an optimal solution for multiple problems.
 
 Valves associated with the molecular sieve can see normal process temperatures from 350 to 360 degrees Fahrenheit with severe spikes approaching the upper limits of most polymer seat materials. The danger this poses to valves is potential deformation of the valve seat when in the closed position. Most standard seats won't recover quickly, if at all, to their normal shape or size under extremes of heat and temperature. This can quickly lead to leaking.
 
 One solution is ordering special seats made of engineered plastic material. While the engineered plastic material seats provide excellent recovery in high-temperature situations and are very durable, there are drawbacks. The seats can be used in ball valve designs but are not suitable for use in a high-performance butterfly valve where more costly metal seats are frequently used. A seat made of an engineered filled fluorocarbon polymer is a better alternative and provides durability with low torque characteristics. In ethanol processing applications where temperature spikes are prevalent, this seat allows the ethanol processor to enjoy extended periods of leak-free valve performance, reduced seat inventory levels and increased safety by reducing the potential for misapplication of replacement seats.
 
 There are a number of shut-off valves associated with the molecular sieve that cycle many times per hour. This creates the question: "How long of an interval can be reasonably sustained before the plant must be shut down for maintenance of these critical valves?" In recent years, some manufacturers have optimized their valve designs by substituting a number of advanced wear part components that dramatically reduce torque requirements while improving wear resistance. This has made it possible for some to increase the standard warranty to up to 1 million cycles (depending on the media). Where extending intervals between maintenance is deemed to be important to profitable ethanol operation, 1 million cycles is now a reasonable benchmark for evaluating valve longevity.
 
 More Problem Solvers

 In addition to the technologies reviewed above, specifiers should be aware of solutions developed in other contexts but readily available to ethanol processors.
 
 Beating noise: When there is a sharp drop in pressure across a steam valve, high decibel noise is generated. This frequently happens in ethanol processing tank valves where an 80- to 90-pound pressure drop can occur between the 150 pounds per square inch steam line and the tank. In these cases, the first concern is meeting Occupational Safety and Health Administration sound exposure criteria for workers around the tanks.
 
 The second concern is damage to equipment. Some solutions for attenuating noise in steam applications include using a global valve with a diffuser or installing expensive baffles in the line to make the pressure drop more gradual. To date, the most cost-effective solution is a rotary segment valve equipped with specialized trim that causes steam to flow through a series of channels to attenuate the pressure drop and dramatically reduce noise. This solution is smaller, lighter and less expensive than other alternatives and reduces noise by up to 18 percent. 
 
 Process and environmental safety: Automatic digital systems for monitoring and testing emergency shutdown and venting valves can dramatically reduce the odds of these critical systems being unavailable during an emergency. Other considerations include specialized valves features like live-loaded stem seals to prevent transient emissions, and polymeric seats with metal carriers that can provide effective shut-off even if the polymer has been destroyed by fire.
 
 Bus networking: Bus networks are used in major processing plants for the operation, monitoring and diagnostics of valves in control loops. With bus networks, ethanol processors can take advantage of software that offers extensive remote valve management capabilities for optimizing process performance and reducing control valve maintenance costs. Bus networks are also used with increasing frequency to network automated on/off valves, which reduces the installation costs of point-to-point hardwiring using 4-20mA, two-wire connections. By networking the valves, wiring and labor costs can be reduced by as much as 40 percent in standard applications and by as much as 65 percent in hazardous areas.
 
 Correctly sized actuators: A major cost consideration in selecting actuators for automated on/off valves is choosing an actuator big enough to do the job, but not so big that the cost is out of proportion with the valve package's worth. This isn't always a straightforward choice because unforeseen process dynamics may require more torque than originally specified. To avoid this problem, some suppliers have specialized technology for detecting any unsuspected dynamic torque situations and analyzing process variables supplied by the system designer.

 
 High-coefficient of flow transportation valves: In addition to tight shut-off and safety, an important consideration for ethanol transportation is coefficient of flow, which determines how quickly product can be loaded on and off of carriers, primarily railroad tank cars. Substantially increases coefficient of flow, allowing tank cars to load and unload dramatically faster and make several more runs per year.
 
 In Conclusion
 The valve industry offers a broad range of solutions to provide ethanol processors with better process performance, more uptime, and optimal plant and environmental solutions. Specifiers should strive to identify suppliers with a depth of technology, manufacturing and channel resources to respond rapidly to the needs of the dynamic and fast-paced ethanol manufacturing industry.
 
 Eric Fillion, Brian Bombard and Bob Mulcahy are technical experts with Metso Automation, a company specializing in automation and information management application networks and systems, field control technology and life-cycle performance services. Metso's main customers are the pulp and paper, power, energy, and oil and gas industries. For more information call (508) 852-0215 or visit <a href="http://www.metsoethanol.com" target="_blank">www.metsoethanol.com</a>.
 
 The claims and statements made in this article belong exclusively to the author(s) and do not necessarily reflect the views of Ethanol Producer Magazine or its advertisers. All questions pertaining to this article should be directed to the author(s).

Critical Ethanol Valve Applications: Technology to Address Productivity and Safety Concerns

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Critical Ethanol Valve Applications: Technology to Address Productivity and Safety Concerns