Steam Boilers are pressurized containers that allow the water to be steamed by heating. Steam boilers are produced according to EN 12952 (for Water Tube Boilers) and EN 12953 (for Flame Smoke Tube Boilers) standards in Europe.
We can collect Steam Boilers under two main titles as
- Fire Tube Boilers
- Water Tube Boilers
but Steam Bıilers; can also be named according to the place of use, type of furnace, type of fuel used, its construction, and boiler pressure class.
Feed Water Control, Level Measurement and Safety
Level Measurement and Safety
The boiler drum is where water and steam meet and separate from each other. The water level here is one of the important parameters to be measured and controlled. For the boiler to operate safely and efficiently, the water level in the drum must be kept constant.
Too low water levels can damage the boiler tube due to overheating as a result of the boiler running dry, causing mechanical damage, that is, melts and collapses. The water, which is given without waiting for the hot boiler pipes to cool, causes explosions.
Another point to note is the high level. Too high drum water level can damage downstream equipment, causing water transport, improper operation of separators, difficulty in temperature control, water carryover resulting in water hammer.
The amount of water entering the boiler should be balanced with the amount of steam released to obtain the constant water level in the boiler. Therefore, it is extremely important to have information about the operating principles, assembly requirements, strengths, and weaknesses of the drum water level control system. Ignoring these issues may result in an improper application, frequent maintenance, unsafe operation as well as low system performance.
On-Off Feed Water Control
During the On-Off feedwater control, the feedwater pump turns on and off by the commands it receives from the level probe. The pump starts when the water level drops to the specified low water level. When the water level reaches the determined high water level, the pump stops.
Modulating Feed Water Control (Single Element Control)
During the modulating feedwater control, a capacitive level probe on the boiler transmits the water level to the controller, and the water level is kept constant by providing the required valve opening by the level controller. The valve used in the system can be preferred as 2-way or 3-way depending on the user. In proportional feed water control systems, it is desirable to have a pump running continuously and a valve proportionally allowing water passage. In addition to this system, control can be achieved with direct variable speed pumps without using valves. However, due to reasons such as the cavitation of the pumps at low frequencies, the most applied and problem-free method in the field is the systems installed with valves.
Advantages and Disadvantages
- In On-Off Feed Water Control Systems, with the operation of the pump, a colder water than the water in the boiler is added to the boiler. This addition can cause variable vapor pressure and flow. In addition, the continuous opening and closing of the pump in the long term causes wear and tear on the pumps.
- On-Off Feedwater control systems are very simple in terms of installation and use.
- On-Off Feedwater control systems are suitable for low capacities.
- On-Off Feedwater control systems are affordable.
- In On-Off Feedwater control systems, a separate pump is needed for each boiler.
- If there is a peak steam draft in boilers using On-Off Feedwater control systems, production may stop and slow down due to false alarms. In addition, water carryover along with steam may also cause water hammer and there is a devastating impact in the installation.