Fuel-gas trip

I noticed, with sinking heart, that the combustion chamber pressure was steadily rising. It rose from 2 to 12 psig, at which point the fuel gas tripped off as a result of the high pressure. The sulfur plant start-up was aborted But what had happened ... 

A less common type of fuel-gas trip to a heater is a low-pressure trip. A pressure transducer generates a milliamp output from a boiler feed-water pump. Should this milliamp output fall below a certain level, the... 

Temporarily place an object in the fuel-gas trip valve that will jam it halfway open when it is activated. 

Expose the thermocouple to a source of heat sufficient to obtain the fuel-gas trip temperature. Check this temperature with a portable potentiometer. 

Observe that the fuel-gas trip valve is actually activated. 

On the boiler that exploded the manual individual burner valves were not closed when the boiler shut down. After the purge period, fuel gas was admitted to the header from remote manual controls in the control room and into the firebox. Low fuel gas pressure tripped the master safety valve after each attempt to pressure the fuel header. Three attempts were made to purge the boiler and on each of these occasions fuel gas was dumped into the furnace through the open manual burner gas valves. On the third attempt a severe explosion occurred. 

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. 

Some heaters also have a low fuel-gas pressure trip on the fuel gas itself. The idea here is that if fuel-gas flow is lost, we do not want it to surge back into the heater too quickly, if it is suddenly restored. 

Same lean gas also supplied to combined asset fuel system from tripped train (< 150 MMSCFD). Fuel gas supply from other operating train minimized. 

The flow of fuel to the boiler should have been slopped automatically when the water level fell to a dangerous level. Unfortunately, the low-level trip failed to function. (Many newer boilers come equipped with backup low-level trips.) The operatingengineer investigating this incident determined that this trip had not been tested for years. He set up the following program to prevent a recurrence. First, the fuel gas control valve was locked into its normal operating position with its hand jack. Then the low-liquid-level trip pot (see Fig. 17-1) was blocked in and drained down. Finally, an operator verified that the pneumatic signal to the fuel-gas control valve fell to zero (this valve was AFC—air failure closes). 

The operating reliability of many process units is impaired because of defective trips. For example, the flame scanner on a furnace will shut off the fuel gas when the scanner no longer "sees" the flame. Too often, the flame is still on, but the scanner s window has become dirty. 

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... 

Eventually, the fouling deposits on the rotor will become so thick that they start to break off, especially if you shut the compressor down for a few hours for minor repairs to the lube-oil system. When the compressor is put back on line, bits and pieces of grayish salt break off, and unbalance the rotor. At 8000 rpm, the high-vibration trip cuts off the fuel to the gas turbine, and the machine is taken off line for repair. 

In many modern instruments, especially the more expensive ones, a flash-back causes a switch of some sort to trip, immediately shutting off the fuel supply to minimize the risk of fire. The switch must be reset before the flame can be relit. More sophisticated instruments incorporate additional sensors related to safety. These include devices to detect the presence of the correct burner head, gas... 

It is interesting to calculate the volume of CO2 emitted by an average car in a year. Suppose the car is driven 10,000 km each year, and while doing so, it consumes 1L of fuel per 10 km hence, it requires 1,000 L a year (a good number of trips to the gas station ). 

In this paper, we have presented a new on-line monitoring system to help oil and gas companies monitor the performance and availability of their machines. This helps in reducing down time and preventing trips. The article presents rules to monitor the performance of the axial compressor and output of the machine, as well as a rule to monitor fuel consumption, which is also applicable at part load conditions. Physics-based availability rules to monitor the wheelspace temperatures and combustion process were also shown. Vibration rules based on a correlation with key parameters as well as a new rule to measure natural frequencies were also introduced. 

There are currently no standards for use of gas detectors for fuel storage installations and no fuel storage installations within the UK where gas detectors are installed. Gas detectors are available but the dispersion of gasoline vapour is complicated and hence effective detection by gas detectors is subject to many uncertainties. Open path detection devices are available and could provide boundary detection at bund walls or around tanks. Liquid hydrocarbon detectors, however, may offer effective detection because it is easier to predict where escaping liquid will collect and travel. There are a number of installations where liquid hydrocarbon detectors are installed. Typical locations would be in a bund drain, gutter or sump where sensors can detect oil on water using conductivity measurement. The detection system may be subject to failures or spurious trips... 

---