Natural gas-powered industrial- and commercial-scale burner-boiler fuel trains need to be carefully designed and managed to satisfy key safety and regulatory requirements — and to meet performance and operational demand. One of the most critical components in the fuel train is the safety shutoff valve and actuator: It allows for flow control of the fuel gas between the source feed and the combustion chamber. OEMs that design and equip these burner systems as well as the facilities that operate them must be aware of developments in fuel train safety-valve technology.
Understanding some of enhancements available for combustion systems will help both equipment manufacturers and end users assess key points when selecting devices for their installations.
Safely Controlling Fuel Flow
Safety shutoff valves can provide both on/off and high/low/off fuel modulation, which allows for the full shutdown of the valve or different levels of modulation of the valve, in terms of open-to-close status. When the burner or boiler is not operating, the valve is in the normally closed position. Valves need to be designed to ensure that when closed, natural gas is not flowing through the pipe train. The current generation of safety shutoff valves can be operated either through an electrohydraulic motor actuator or with a solenoid operator. The burner management system (BMS) is a set of devices used to safely start up, operate and shut down a fired vessel. It monitors and controls various equipment while heating a vessel to a desired temperature setpoint. A range of safety shutoff valve options is available for the industry with myriad features and performance characteristics. Whether they are operating direct-fired heaters, industrial furnaces, ovens or kilns, or even residential or commercial uses, burner and boiler operators share a number of concerns and performance requirements as they seek the optimum valve solution for their operations. They include:
- Safety and reliability.
- Energy efficiency.
- Ease of installation.
Safety and Reliability. They seek valves that satisfy key global regulations and standard body requirements such as NFPA and CSA as well as the emerging Combustion Safety Devices standard (CSD-1) being adopted in many U.S. states. Reliability in valve operation focuses on the safety valve’s ability to support burner operation in both low and high pressure scenarios. In the low pressure scenario, the valve supports reliable burner operation through high flow rates, which ensure that the burner is not starved of fuel. In high pressure scenarios, the valve’s high operating pressure rating ensures the system can be rated to support increased pressures, and its high close-off pressure ensures safe shutdown during unexpected system pressure spikes. In addition, valves need to deliver this reliability in extreme environmental conditions. Remote locations such as petroleum extraction wells and pipeline pumping stations can experience temperatures as low as -40°F (-40°C). Yet, these locations still require a reliable valve function to ensure burners operate correctly.
Energy Efficiency. Controlling fuel usage as much as possible also is a key requirement. Many boiler and burner system OEMs are looking for safety valve systems that can reduce pressure drops across the entire fuel train. A high/low/off actuator offers a cost-effective way to adjust the firing rate, which saves energy based on boiler demand. Boilers and burners have varying fuel demand cycles during the course of operation. As a result, users also seek systems that can provide high turndown ratios through fuel and airflow throttling versus a simpler on/off functionality. This helps the entire system deliver only the amount of fuel needed during the burner cycle.
Ease of Installation. Form factors for safety valves also are recognized as an important issue for both boiler and burner OEMs and end users/operators. The time and costs associated with installing safety valves can be significant. This is especially true if the valves are replacement devices that need to be fitted into existing tight boiler rooms or industrial equipment spaces. Valves with a compact footprint that are engineered for ease of mounting into existing piping systems can help reduce both installation time and the need for additional connecting devices. Given these key concerns, safety shutoff valve manufacturers have been introducing valve technology designed to provide a more complete solution for both new burner and boiler installations. The valve technology also serves as an effective replacement for legacy devices at the end of their operational lives.
Safety shutoff valves can be used for burner-boiler and power generation applications, among others. Photo credit: Bibica / iStock / Getty Images Plus / Via Getty Images
Simplifying Procurement and Compliance
As boiler manufacturers increasingly move from regional to global operations, obtaining components that comply with all of the relevant standards — no matter where the system is installed — is quickly becoming an important requirement. New valves that meet all global requirements simplify design, planning and procurement across all regions. As mentioned previously, global OEMs are looking for product lines that are certified compliant with standards such as CSD-1, NFPA, UL, CSA, FM, RoHS and EN161. Safety valve systems that provide this kind of comprehensive certification can help reduce the cost and complexity of creating fuel-train solutions that safely comply with regulations in multiple regions and jurisdictions. Such valves also may include a number of features designed to improve reliability, energy efficiency and installation challenges, including:
- Minimized pressure drop.
- High close-off pressure ratings.
- Valve proving.
- Compact design.
Minimized Pressure Drop. As natural gas flows through the fuel train, pressure drops are incurred through any component or device (i.e., elbows, bends or valves in the pipeline). This can be an issue for the user when inlet pressure is low yet the burner heat output needs to be maintained in order for the boiler or any unit operation to function. In a typical fuel train, the highest level of pressure drop occurs through the double safety shutoff valve. Most often, the double safety shutoff accounts for more than 65 percent of the fuel gas pressure drop incurred through the entire fuel train. Valve solutions include motorized actuators, replacing solenoid-actuated systems. Motorized valve actuators typically offer better flow and higher pressure ratings. This helps ensure safe and stable control of gas flow through the valve with minimized pressure drops, improving burner reliability.
High Close-Off Pressure Ratings. While valves with high flow ratings are desired — to ensure reliable burner operations in low pressure conditions — burner manufacturers often seek valves with high close-off pressure ratings. Such valves can reliably shut off flow during high upset pressure conditions in the gas supply. A valve that has both high flow ratings and high close-off pressure ratings means it can perform reliably in low pressure applications common in densely populated metropolitan areas as well as high pressure applications subject to high system pressure spikes. (Such conditions are typical in remote locations within Canada, Minnesota or the Rockies.)
Valve Proving. Valve proving is a protocol that opens and closes the two main shutoff valves in the proper sequence and monitors pressure in the gas pipe between the two safety shutoff valves. This ensures there is no gas leakage across the train. Valve proving helps increase energy efficiency by eliminating unburned gas emissions through the vent while also reducing or eliminating vent piping.
This can be particularly useful in limited-space or finished settings where new boilers are installed or existing valves are upgraded. Without a valve that supports valve proving, it is necessary to install vent piping that exhausts any gas trapped in the valve to a safe location. In some facilities, this can require installation of hundreds of feet of vent piping. Valve proving eliminates those extra cost and installation issues. Valves supplied with published gas capacities enable users to commission and run a valve-proving protocol on the fuel train.
Compact, Monoblock Design. Some modern safety valves are smaller than previous designs and can be mounted in any position. Offering a lighter weight design, some designs incorporate features such as a threaded end connector (rather than the valve), so the same valve can be used with either NPT or ISO end connectors. One monoblock design allows two valves to be placed in a single body casting.
Valve technology uses motorized actuators to provide broad pressure ranges. Photo credit: RealPeopleGroup / E+ / Via Getty Images.
Improved Safety and Reliability
The high close-off pressure rating offered with the valves means they will reliably shut off flow when subjected to 75-psi spike pressures — thereby reducing the need for additional safety components such as relief valves and flame arrestors. The technology is rated to continue functioning in harsh environments, with temperatures ranging from -40 to 150°F (-40 to 65°C). Many of the valves include built-in particle strainers, aiding in removing debris that might damage the valve or other parts of the fuel train. In addition, the valves can be used with NEMA-approved Type 4 enclosures, safeguarding against outdoor elements such as rain, debris and dirt.
Obtaining components that comply with relevant standards, regardless of where the system is installed, is becoming increasingly important. Photo credit: Emerson
The higher flow rates of the valves reduce the naturally occurring pressure drop as natural gas progresses through the fuel train. In effect, this increases energy efficiency by providing the required gas pressure to the burner. It also ensures an uninterrupted heat supply even when gas pressures are low. The designs integrate with valve-proving systems, devices that electronically check valve-seat integrity and eliminate the need for vent piping. With the elimination of vent piping, greenhouse gas emissions associated with unburned fuel release are reduced. In addition, replacing solenoid-activated on/off valves with motorized actuators makes it possible to cost effectively reduce the firing rate. An actuator can be placed in the low or high fire position, using only the energy needed. This avoids the waste that can happen when the boiler’s demand does not require firing at 100 percent.
Monoblock designs simplify installation. Photo credit: Emerson
Fewer, More Cost-Effective Components
The increased flow allows system designers to reduce the size of the components they use when designing a fuel train. For instance, instead of specifying a 2” pipe, designers can use a 1.5” size and potentially downsize all additional fuel-train instrumentation, including the regulator and butterfly valve. Some valve product lines have the thread integrated within the valve body, so users must stock as many as eight valve bodies to cover the range of valve sizes. Valves threaded only in the end connector make it possible for OEMs, installers and end users to stock fewer body sizes along with the associated end connectors to achieve the full range of pipe sizes.
The use of end connectors eliminates the need for a pipe union. Bolting areas are placed in an area that is accessible with a wrench. In addition, the motorized actuator will be backward-compatible with the legacy valve. This reduces the piping rework often required with field retrofits and replacements.
Some valve products can be mounted in 360 degrees, meaning they can be placed in any orientation, even upside down, if needed. A smaller, lighter weight footprint makes it easier for installers to place it in retrofit situations or tight spaces.
In conclusion, fuel-train safety-valve manufacturers have been investing time and resources to provide improved options for boiler and burner OEMs and end-users. Some provide comprehensive certification with globally relevant regulatory and standards requirements to allow global companies to stock universal components. Valve technology that uses motorized actuators to provide wider pressure ranges and to provide reliable operation in both high and low pressure applications can simplify procurement.