Questions and answers on Thermic fluid heaters


What is Thermic fluid heater?

A thermic fluid heater, also known as a thermal oil heater or hot oil heater, is  used to heat a process fluid to a specific temperature using thermal energy. It operates by circulating a heat transfer fluid, commonly referred to as a thermic fluid or thermal oil, through a closed-loop system.

 What is meant by heat transfer fluid in Thermic fluid heaters?

 A specialized heat transfer fluid, often a mineral-based or synthetic oil, is used as the medium to transfer heat. It has high thermal stability and a high boiling point to ensure efficient heat transfer and safe operation at elevated temperatures.

 What type of combustion chamber is used in Thermic fluid heaters? & how heat generation starts?

 A thermic fluid heater is equipped with a combustion system, which can use various fuels such as natural gas, diesel, heavy oil, coal, or biomass. The fuel is burned in a burner assembly to generate heat.

 How does heat exchanger takes role in Thermic fluid heaters?

 The heat exchanger is the core component of a thermic fluid heater. It consists of a coil or tube bundle immersed in the thermic fluid. The hot combustion gases pass through the coil, transferring their heat to the fluid. This process raises the temperature of the thermic fluid.

The heat generated from the combustion process is transferred to the thermic fluid. The hot flue gases and combustion products flow over the surface of a coil or heat exchanger immersed in the furnace. The coil or heat exchanger is filled with the thermic fluid, which absorbs the heat from the hot gases.

 How does circulation of thermic fluid happens in Thermic fluid heaters?

 The thermic fluid, now heated, circulates through the coil or heat exchanger via a circulation pump. The pump provides the necessary pressure to move the fluid through the system.

 How does heat is being utilized from Thermic fluid?

 The heated thermic fluid carries the absorbed heat to the point of application or process equipment where heat is required. This could be reactors, dryers, presses, or any other heat-consuming equipment.

At the point of application, the thermic fluid transfers its heat to the process equipment or medium, raising its temperature as needed. The thermic fluid's temperature decreases as it gives up its heat energy to the process.

The cooled thermic fluid returns to the heater through a separate return line. In the heater, the thermic fluid is reheated by passing through the heat exchanger or coil, where it once again absorbs heat from the combustion process.

 What is the function of expansion tank in Thermic fluid heaters?

 A thermic fluid heater system typically includes an expansion tank to accommodate the expansion and contraction of the thermic fluid as it is heated and cooled during operation. It helps maintain the desired fluid volume and prevents excessive pressure build-up in the system.

 What is the significance of Control system in Thermic fluid heaters?

 A control system is employed to regulate the heating process, including temperature control, fuel supply, and safety features. It ensures precise temperature control and monitors various parameters to maintain safe and efficient operation.

The temperature of the thermic fluid is controlled and maintained within a desired range using temperature control systems. The system may include temperature sensors, control valves, burner modulation, and circulation pump speed control to regulate the fluid temperature.

 What are the various applications of Thermic fluid heaters?

 Thermic fluid heaters found applications in chemical, pharmaceutical, textile, food processing, and oil and gas.

 What are the main advantages of Thermic fluid heaters?

  • High temperature accuracy,
  • Efficient heat transfer,
  • Versatility in fuel options, and the
  • Ability to provide uniform heating over large areas.

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How do you calculate the work done & specific steam consumption of a back pressure steam turbine?


In back pressure turbines, steam just inters through HP valves & exists through exhaust, no any bleed or condensation is done.

The efficiency of the back pressure turbines is more as compared to condensate & condensate cum extraction steam turbines. However specific steam consumption of back pressure turbines is very less as compared to above both type of Turbines

 How do you calculate the work done per kg of steam?

 Let us assume 1 kg/sec of steam is entering into Turbine whose enthalpy is H1 kcal/kg & existing from turbine at enthalpy H2 kcal/kg

Then, work done per kg of steam is given as =(H1-H2) kcal/s

Or 4.18 X (H1-H2) KW, since 1 KJ/sec = 1 KW

 How do you calculate specific steam consumption of a back pressure Turbine?

 Specific steam consumption is defined as the amount of steam consumed to generate 1 KW of power

 SSC = 860 / (Difference in inlet & exhaust enthalpy)

 i.e 860 / (H1-H2)

 A back pressure turbine is operating at pressure & temperature 64 kg/cm2 and 490 deg C respectively, the exhaust steam at pressure 2 kg/cm2& temperature 140 deg C is being used for process.Calculate the work done and specific steam consumption?

 Enthalpy of inlet steam at pressure & temperature 64 kg/cm2 and 490 deg C  = 809 kcal/kg

 Enthalpy of inlet steam at pressure & temperature 2 kg/cm2 and 140 deg C  = 660 kcal/kg

 Work done = (809-660) = 149 kcal/sec

Or 4.18 X 149 = 622.82 kJ/kg or 622.82 KW

Specific steam consumption SSC = 860 / (Difference in inlet & exhaust enthalpy)

SSC = 860 / 149 = 5.78 kg/kw or MT/MW

 A back pressure turbine having inlet steam enthalpy and exhaust enthalpy 780 kcal/kg & 580 kcal/kg, then calculate the specific steam consumption of that Turbine?

 SSC = 860 / (Difference in inlet & exhaust enthalpy)

SSC = 860 / (780-580)

SSC =4.3 MT/MW

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What are the various interlocks used in Boilers??


1.What do you mean by Interlocks?

 Interlocks are the programmed or hardwired control system made to protect the machine or system from damages or disturbances

Interlocks and protections involve sensors, cables, wires, local push buttons, logics, timers, probes etc.

 2.What is the significance of interlocks?

 Significance of interlocks;

  • To protect the system against damages/disturbance
  • To protect the equipment
  • To avoid damages to the man and machine
  • To avoid operation disturbances

 3.What are the various protections used in Boilers?

  • High drum level trip
  • Low drum level trip
  • High main steam pressure trip
  • High positive draught trip
  • High negative draught trip
  • High main steam temperature trip

 4.What are the various interlocks provided for Boiler feed pumps?

 Boiler feed pumps trip on acting following interlocks

  • Low de-aerator level
  • High bearing vibration
  • High bearing temperature
  • High feed water temperature at suction
  • High drum level

 5.Write a brief note on Boiler interlocks

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Sl No.




High drum level-FD fans trip followed by fuel feeding system & ID fans

To avoid carryover of water particles in steam

To avoid thermal shock to super heater coils


Low drum level-FD fans trip followed by fuel feeding system & ID fans

To avoid over heating of pressure parts due to lack of water


FD fans trip-Fuel feeding system trip

To avoid jamming of fuel feeding system & grate


High furnace draught-FD & SA fans trip

To avoid furnace explosion


Low furnace draught-ID fans trip

To avoid explosion of ESP & related ducts to vacuum pressure


High main steam pressure-Boiler trips (FD & fuel feeding system)

To avoid failure of pressure parts due to high steam pressure


High main steam temperature-Boiler trips (FD & fuel feeding system)

To avoid failure of pressure parts due to high steam temperature


PA fan trips- Fuel feeding system trips

To avoid jamming of fuel feeding system


High main steam pressure-Start up vent CV auto open

To avoid failure of pressure parts due to high steam pressure


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