Information     Organic Water Treatment Chemicals Steam Boilers, Cooling Towers, Hot And Chilled Closed Systems Fuel Oil Treatment (Home of D.M Concentrate) Boilers Questions & Answer Question: Emergency low boiler water level You are an officer on watch, & finds the boiler water-level gauge glass to be empty & the burner firing...What is your course of action? (Assuming the gauge glass to be clear & good working order) Answer: Normally a boiler is provided with two independent sensors for emergency low water level burner cut-outs. So this would never happen. However, if it does, don't take any take chances! Shut off the burners immediately! Before you start raising the level in the boiler you have to find out if any part of the furnace walls has been overheated. If you raise the level over a glowing steel-wall then the boiler might produce more steam than the safety valves can handle and a nasty explosion would be the result. Question: Differential pressure transmitters for the steam drum level Way is the high pressure leg of the transmitter connected to the water side and the low-pressure leg connected to the steam side? Answer: The signal from the transmitter ought to increase when the water level raises and decreases when the level falls. Furthermore the signal shall be zero, and give impulse to stop the burner, in case of transmitter malfunction, power failure or cable breakdown. Both requirements will be fulfilled if the transmitter is mounted with the high pressure measuring point connected below the lowest water level and the low pressure measuring point connected above the highest water level. The output will increase when the level is raised. To compensate for the water column in the reference leg the output signal's zero-point has to be elevated. This is the common method. If the transmitter is swapped, with the low pressure side to lower end and the high pressure side to upper end, then the signal will decrease when the level is raised. This signal can be used to control the level as well, but the signal can not be used to stop the burner for emergency low level in case of power failure or cable breakdown. This system requires an extra sensor to trip burner at emergency low water level. One can of course use the emergency high water level alarm to stop the burner, but this is not correct. The emergency high water level shall stop the feed water pump and whenever applicable stop the steam turbine, but not the burner. Question: Fluctuating boiler water level The feed water control valve is fully open and the water levels fluctuate at normal boiler load. Answer: Check if: the control valve really is fully open by means of the hand-maneuver device. all stop valves in the line are fully open. the suction filter to the feed water pump is satisfactory clean. the feed water pump discharge pressure is sufficient. the feed water control valve pressure drop is normal. (>=2 bar or >=30 psi) If all these are fund to be in order, then you should recalculate the control valves kV-value (CV-value). Under-sized control valves do exist, even though over-sized control valves more often cause malfunction of automatic control loops. The tuning of the controller (s) is dependent on the system you have, but do not even try to tune the control loops until the above criteria are fulfilled. Question: The burner starts and stops very often The burner starts and stops very often, sometimes every second minute. An alarming temperature-raise has been observed in the combustion air fans electric motor. Answer: Increasing the burners turn down ratio would be a nice solution, but it's not always possibly. Run the burner in minimum load, i.e., prevent the burner from increasing the load just after the burner start. Install a five to ten minutes' time-delay in the fan-motor stop function. Then the fan will continue to run during the shortest burner stops and the combustion air fan motor will get a little rest from the start current. Question: Most likely source of errors In which part of a boiler control system is it most likely to get a failure. Answer: When you have problem with a boiler control system you should keep in mind that most faults occur outside the control cubicle, but on the other hand, your problem might not be among the most common. Statistically calculated faults in control systems. Transmitters and sensors 40 % Actuators  25 % Controllers 10 % Loss of electric power 5 % Others  20 % Question: Open steam valves slowly Why has a steam valve, or at least a big steam valve, to be opened slowly? Answer: If you have a one liter of water standing in the pipe just after the valve and open the valve too fast, then you will get a projectile of one kg rushing down the pipe. At next valve, bend or other obstacle the speed of the water mass will be converted into pressure. You can hardly imagine the damage this energy can cause. Thermal stress is an other reason to be very cautious and drain out water carefully when you open a steam valve. A large steam valve ought to have a small by-pass valve to simplify preheating of the pipe. Question: Low viscosity fuel for high viscosity burners Our boiler plant is designed to be fired with heavy fuel oil of 600 CST @ 50°C. Would it be safe to run it on Gas Oil of 7 CST @ 40°C? Answer: Well, this is a question for the burner maker. Don't forget to ask them too. It is very important that the fuel oil heaters are bypassed when firing Gas Oil or Diesel Oil. These fuels must never be heated above their flash-point. For a steam atomized burner you have to switch over to compressed air atomizing since light fuels must not be atomized by means of steam. This burner will probably fire the fuel without any problem since they normally are designed for fuel viscosity between 10 and 20 CST. A rotary cup burner, on the other hand, might give some problem with the flame since this atomizing method normally require a fuel viscosity of about 25 to 60 CST. In the event of failed ignition, gas-oil is more likely to cause an explosive mixture than heavy oil. However, a dangerous situation should never occur if the procedure for such failed ignition is followed. Upon two consecutive failed ignition attempts, a thorough investigation into the cause should be sought and the furnace correctly purged inline with the manufacturers and ruling classification society's requirements. N.B. 7 CST @ 40°C = 5.5 CST @ 50°C. The viscosity's of lighter fuels are normally given at 40°C and the viscosity of heavier fuels at 50°C, 80°C, 100°C or even higher temperature.