There were two boilers in the boiler room in my training plance which were assembled in Machmar Boilers Inc, Malaysia. Although some fabrications have been done by them; burners, flow meters and pressure gauges had been imported from England and Switzerland. The boilers are in size 800/150 and includes CH7-38F type burners. The capacity of each boiler is 8000kg /hour.
The safety is very important than any other operations which should be considered very carefully when handling a boiler. Machmar boilers have been equipped with twin safety valves. One safety valve has been set to blow off at 150 psi which is below to design pressure, while the other has been set to blow off at 152 psi which is below to the design pressure (155 psi). These safety valves have been padlocked to prevent unauthorized adjustments. 155 psi is a somewhat higher pressure which is selected to allow for possible down-rating with age. The boiler is usually operated in a range of 110 – 130 psi.
The Boiler design
The Mechmar boilers are fully automated steam generating units of the three pass fire tube model which can be used for high efficiency operation. The three pass fire tube operation can be described as follows. The burner which consume Furnace Fuel Oil, fires into a large cylindrical combustion chamber which is closed at one end. The unit is so designed that the flame reverses upon itself before entering the convention tubes. This three pass mechanism ensures intimate mixing of the fuel vapour and maximum combustion efficiency.
Within the convention tubes special spirals have been inserted. These are manufactured using heat resisting steel. This feature is used for two purposes.
1. To increase the heat transfer rate in the convention tubes (fire tubes)
2. To allow the flue gas temperature to be controlled by changing the length of spiral.
The three pass mechanism can be describe as the first and second passes take place in combustion chamber while third pass takes place in convention tubes.
Mechmar boilers have been insulated well using glass wool layer. Because of this feature the base and boiler casing will be only slightly above room temperature which prevents convection heat transfer to atmosphere. So the heat loses is very low.
Water level control
The water level is one of critical parameter in boiler operation. The water level of in the boiler is monitored using two water level control (There are two, incase of one fails to function well there is the other to back up the situation) mounted externally on the side of the boiler.
The safety valve is the most important valve on the boiler. Safety valves prevent dangerous over pressurization of the boiler. This valve is set to lift just above the required operating pressure of the boiler, and will normally come into operation only if the pressure controls fails. The valve is set by the manufacturers and requires no adjustment. But in annual boiler test inspector check the valve and approve for next year. There is a pressure control system in boiler. That system automatically switches between high and low firing status of burner to keep boiler pressure at working pressure. If this system fails there are safety valves to protect boiler and staff. A one safety valve suddenly opens when boiler pressure passed 150 psi. Other safety valve suddenly opens when boiler pressure passed 152 psi. We can keep confidence on boiler safety system because of the proper pressure control system and there are two safety valves in case of pressure control system fails. The last boiler test has been done in 13th of May, 2006.
Feed Water Treatment
The Total dissolved solids (TDS) level of boiler water is another critical parameter Water. If TDS level is exceed its limitations, scaling and pitting are occurred inside the boiler which reduces heat transfer efficiency of boiler. The feed water comes through a softener unit where some chemicals are used. Softening reduces the sedimentation and additional chemicals (e.g.D.M.4.1, Alkatreat) reduce the scaling and pitting.