Fuel-gas shutoff

One of the most common safety trips is the automatic fuel-gas shutoff. We have this at home on our furnaces. We ignite the pilot light manually. The pilot light heats a thermocouple. The milliamp output from this thermocouple opens the fuel-gas valve to the main burner. The gas in the main burner is ignited from the pilot-light flame. Should the heat from the pilot light diminish below a certain point, the fuel gas to the main burner, as well as to the pilot light, will be shut off. 

A permanent and ready means for making tightness checks of fuel gas shutoff valves is typically required per NFPA 86 (sect. 5-1.23). This practice is recommended for the oxygen safety shutoff valves as well. 

One of the most common safety trips is the automatic fuel-gas shutoff. We have this at home on our furnaces. We ignite the pilot light... 

An Isolation Valve (BV200) is required by NFPA 86 (sect. 4-2.4.1.1 and sect. 5-2.2). The purpose of the isolation valve is to provide a manual shutoff for maintenance and emergency conditions. Therefore, the valve must be located in a position where a hazardous condition will not impede access to the valve by plant personnel. A quarter-turn ball or butterfly valve with usual indication of valve position is required by NFPA 86 (sect. 4-2.4.1.2). The valve should include a locking feature so that the supply of fuel gas can be locked-out/tagged-out during maintenance operations. 

The fuel gas safety shutoff valves are required by NFPA 86 (sect. 5-7.1.2) to shut off the flow of fuel gas in the event of any unsatisfied interlock (e.g., low or high flow of the fuel or oxygen, flame failure, high furnace temperature, low burner cooling water flow, loss of furnace ventilation, etc.). 

At least one of the two safety shutoff valves (on the fuel gas flow run, and on the oxygen flow run) must have a Limit Switch (ZSC) (or similar means) that can be used to prove that the valve is in a closed position during the furnace purge interval per NFPA 86 (sect. 5-4.1.2.1 and 5.1.22) when the burner system has a heating capacity equal to or exceeding 400,000 Btu/hr (120 kW). At least one of the two safety shutoff valves (on the fuel oil flow run) must have a Limit Switch (ZSC) (or... 

Building Provide fuel gas supply lines with seismic-actuated shutoff valves. 

With these waste heat boiler problems—managers with no boiler training, water systems and hot gas shutoff systems inadequately designed, and no operators in attendance—it might be advisable to select an alternate heat recovery system to reduce fuel consumption. 

Gas turbines should be installed with automatic fuel shutoff valves. Locate cooling towers far away from process units. Whenever possible, maintain cooling water pressure more than process stream pressure, at the coolers. Install gas detectors at the top of cooling towers, and an automatic shutdown system for cooling tower fans, in case of gas detection. Boiler and other utilities should be located far away from process facilities so that they will not be exposed to fires and explosions originating in the process plants. Install deflagration or detonation arrestors in low-pressure fuel gas systems connected to atmosphere or fired systems. 

Fuel gas shall not be used from cylinders through torches or other devices which are equipped with shutoff valves without reducing the pressure through a suitable regulator attached to the cylinder valve or manifold. 

Gas Pump Control Shutoff Gas stations employ fuel pumps that are designed to stop flow of gas when the car s gas tank is full. When the gas pump control fails to function, the car s gas tank is overfilled. The fuel pump shutdown represents an example of a protective system operating in high-demand mode, as there are several demands on the fuel pump shutoff a day. 

The control scheme on the furnace is set to regulate the flow of fuel gas (fg) based on the measured tenperature of the exit oil stream (Stream 2). A ratio flow controller adjusts the flow rate of air so that a constant air/fuel ratio is maintained. An oxygen analyzer measures the excess oxygen in the flue gas and adjusts the set point of the ratio controller to maintain the desired air/fuel ratio. A flow alarm is also present to detect a low flow condition in Stream 1 and activates a solenoid shutoff valve to... 

A few days ago there was a process upset in which the oil flow to the fired heater was momentarily interrupted. This interruption triggered the shutoff valve, which closed the fuel gas line. The flow of Stream 1 resumed its normal rate after about 30 seconds, at which time the fuel gas solenoid valve opened and the flow of fuel gas resumed. During the upset, the flow of air changed in proportion to the fuel gas flow. 

Safety shutoff valve — A normally closed (closed when de-energized) valve installed in the piping that closes automatically to shut off the fuel or atmosphere gas in the event of abnormal conditions, or during shutdown. The valve can be opened either manually or by a motor-operator, but only after the solenoid coil or other holding mechanism is energized. 

An example is a vehicle driving away from a gas pump, catching a fuel hose, and starting a fire. If the shutoff is at the pump, it would be difficult to approach and shut off the fuel. 

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