Control And Regulation Of A Boiler

A sufficient number of measuring devices is necessary to be in the boiler for its safe, reliable and economic operation. The main meters of the boiler are:

  1. Manometers to measure pressure of the feeding water, steam in the drum and the main lines, gas and mazut;
  2. Devices of water level reading;
  3. Thermometers to measure temperature of the feeding water, perheated steam and removed flue gas;
  4. Flow meters measuring yields of the steam (boiler output), feeding water and fuel;
  5. Draft gauges measuring thinness at the top of the furnace and boiler smoke ducts;
  6. Smoke analyzers measuring amounts of CO2 and O2 in the flue gas.

Mode of the boiler operation, if all the parameters of the steam, feeding water and flue gas are not altering, is called settled. Having changed the steam demand, the settled operation conditions of the boiler are deranged and steam parameters begin to alter. In order to restore them it is necessary to change the amount of supplied fuel, air, feeding water, draught and so on. Boiler regulation is called manual, if the mentioned changes are carried out by a man. However, in the modern steam boilers these parameters alter so rapidly, that manual regulation is almost impossible, so the facilities for automatic regulation protection blocking of the boiler operation are used.

The regulation system of the drum boiler is divided into several parts. The main ones are of burning process and feeding. The principal parameter, giving an impulse to regulate the boiler combustion process, is steam pressure depending on the boiler loading. Increasing the steam demand, pressure decreases and a regulator should increase the supply of the fuel and air into the furnace. Blowing intensively the thinness in the furnace top decreases, so this is the impulse constraining the guide device of a suction fan to increase the amount of the removed smoke. The process is of a reverse direction, if the steam demand decreases.

Safe operation of the drum boiler depends especially on the suitable water level in the drum. The settled level indicated that the steam amount supplied to the customers corresponds to the feeding water level. So, drum water level is the basic impulse to adjust the boiler feeding. However, water level in the drum also depends on the other factors, so regulator of the feeding water amount supplied into the boiler receives three impulses mostly: the water level in the drum, the amount of produced steam and the quantity of supplied feeding water.

Some more regulators of fuel preparation, blowing through ant other processes can be arranged in the boiler.

Principles of the single-pass boilers adjustment rather differ from those of the drum boiler regulation. In the single-pass boilers the processes are much more rapid, in addition, closely connected among themselves, so their regulation system can not be divided into independent parts.

Every boiler must contain not less than two emergency valves-basic and control. Increasing boiler pressure more than permissible, emergency valves must open, let out a part of the steam and pressure. Decreasing to normal they close again. In the boilers with the pressure more than 4 MPa indirect acting pulsed emergency valves are installed.

Outburst emergency valves are arranged at the top of pulverised fuel-fired furnace of the boiler and in smoke ducts. They open when pressure in the boiler or smoke ducts increases, so protecting the boiler masonry from falling into pieces when the mixture of fuel and air bursts.

Failure warning devices prevent the staff on duty of inadmissible alterations of the basic parameters. In the drum boilers signalling indicators (sound and light) of water level, superheated steam temperature and alteration of feeding water pressure are arranged.

Blocking appliances are necessary for the starting and stopping of the equipment, so that due to staff errors the procedure order would not be lumped together. For example, blocking ones prevent the altering of the procedure of installation combination, putting boiler in the motion: at first, it is necessary to set suction fans into the motion, later-blowing ones and only then the equipment of the fuel supply can be set on. Blocking equipment stops blowing fans, the fuel supply, if suction ones are out of order or stop.

In the boiler house a regulation panel is assembled where the devices of the boiler itself, automatic regulators, protection, blocking equipment operation control and measuring devices are mounted. A control panel with switches commutators of remote control and so on is arranged before this panel. At the panel the place of the boiler stoker is located, from which he is observing and, if it is necessary, regulating the operation of the boiler and automatic regulators.