What is a boiler and what does an industrial boiler do? How can we do the combustion control in a boiler?

What is a boiler and boiler control system?

A boiler is used for many industrial applications, this device is capable to produce steam or vapor. The produced steam would be used for many purposes it is mostly used for turbine propulsion and also as a heating medium. A boiler can be considered as a vessel that has water and it can transfer heat from a fuel source into steam, the fuel source could be oil, gas, or coal. This produced steam is used for many industrial operations like it can be used to run production equipment or to provide heat. A boiler control system is used to transfer the energy into and out of the boiler is done. The boiler inputs will be fuel and the outputs are steam, radiation, blow-down.


How does a boiler work?

A boiler would convert water into steam by using a fuel source and this steam will be used for many applications. The steam that is produced can be converted back to the water, if the steam is converted back to water then it is called a closed system. In certain cases the steam will be contaminated and we won’t be able to use it, so we won’t be able to transfer the converted steam into the boiler and this system is called an open system.

How to do the boiler control and why we need boiler control

In order to control a boiler, we must regulate certain quantities such as

  • Fuel /air ratio – in order to maintain optimal combustion conditions
  • Water flow must be regulated in order to match the steam flow from the boiler
  • Steam flow and pressure to regulate the heat input
  • Combustion chamber pressure
  • Safety combustion

Need for boiler control

  • It would increase uptime and availability
  • Boiler safety can be maintained
  • Operating costs can be controlled
  • It can reduce flue gas emission

By the boiler control, we can maintain the proper mass flow balance of feed-water and steam flow, the firing raters, can be varied according to the plant’s steam requirement. We can ensure complete combustion while minimizing the excess air over the full operating range of the boiler.

In the industrial boiler control system, it utilizes certain control strategies they are

Steam header pressure control

This would check the steam header pressure so that it can provide the load demand for the boiler.

Feed-water control

This is the regulation of the water to the boiler drum, it would provide proper control for the steam production and feedwater entering the boiler. In order to achieve proper boiler operation, the level of water in the boiler must be maintained at a certain level, if this level is decreased then it would uncover boiler tubes and tubes would be overheated. The feed-water control would increase the response of the system, and also we can achieve accurate control and maximum system stability.

How to do a boiler combustion control?

Combustion control in a boiler can be done in two different ways they are fuel control and combustion air control. While doing the boiler combustion control we need some hardware such as ON/OFF controls, positioning systems, and metering control systems. We must do purging before combustion, purging ensures that there are no lingering combustible materials inside the unit. During combustion control the fuel and air to the boiler are regulated, the fuel/air mixture must be right under all dynamic load conditions. There are other combustion control systems to ensure safe operation and they are gas BTU adjustment, on-line switching between fuels, duel fuel firing, Low gas header pressure override.

Mostly to control the combustion automatic control system is used rather than manual control, we won’t able to control the combustion manually by using manual control. The automatic control system can maintain the fuel to air ratio to a furnace in a proper manner and also can maintain constant steam pressure. The combustion control would vary according to the fuel used, but for and the fuel used we must regulate certain aspects like air supply, fuel supply, the ratio of fuel to air, and flame safety.

There are two types of the combustion control systems and they are positioning and metering.

Position type control

This type of combustion control is designed to control according to the change in steam pressure. The major components for this process are a master steam pressure controller, fuel control valve with cam for oil/gas or feed control drive for coal, combustion air fan inlet vanes/ outlet damper operator.

Metering type control

The components of this type of combustion control are almost the same as position type except, it has a fuel flow measuring device and airflow signal. The fuel-air ratio is controlled by a relay. It can adjust the fuel-air ratio.

Hardware used for combustion control

ON/OFF control

This is mostly used in small water tube boilers. If the pressure drops, fuel and air will be fed into the boiler at a determined rate until the pressure would reach its normal level.

Positioning systems

This would respond to the changes in header pressure by positioning the forced draft damper and fuel valve to a predetermined alignment.

Metering control system

The system control is regulated according to the measured fuel and airflow. This would maintain the combustion efficiency for a wide load range and for a long period of time.

How can we calculate the boiler efficiency?

Boiler efficiency is related to the output energy of the boiler to the input energy of the boiler.

Boiler efficiency = Heat exported by fuel / Heat provided by the fuel

The amount of air to the boiler must be controlled to get proper boiler efficiency, if the air is more, then it would cool the furnace and the heat will be wasted. If the air is less, then it would badly affect the combustion.

What are the requirements of a good boiler?

  • Safety – the boiler must be safe during the operating conditions
  • Accessibility – the parts of the boiler must be accessible for repair and maintenance
  • Capacity – it must be capable to supply steam according to the requirements
  • It must be efficient enough to absorb a maximum amount of heat produced due to the burning of fuel in the furnace
  • Simple construction
  • Joints of the boiler must not be exposed to flames
  • Less maintenance

What are the disadvantages of boiler?

  • It needs quick responding control
  • Level of the water in the boiler must be kept 50% of the height

What are the applications of a boiler?

  • It can be used for power generation, it can generate mechanical or electrical power by using the steam
  • It can be used for heating, the produced steam can be used to produce hot water
  • It is used in the industrial process the produced steam is used for sizing and bleaching, it is used in textile and chemical industries, and lot more.