Effect of moisture content in steam Turbines

Effect of moisture content in steam Turbines

 When steam passes through a turbine, it undergoes expansion and releases energy, which is harnessed to generate power. However, if the steam contains water droplets or moisture, it can have detrimental effects on the turbine blades. As the steam expands and flows through the turbine stages, the droplets can impinge on the blades, leading to erosion, pitting, or damage.

 The churning effect typically occurs in the last few stages of the turbine, where the steam is at lower pressure and velocity. At these stages, any remaining liquid particles in the steam are prone to separation from the gas phase and can cause erosion on the turbine blades.

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 Moisture content in steam  leads into the following problems:

 Erosion: The high-speed impact of liquid droplets on the turbine blades can cause erosion, leading to damage and reduced efficiency over time. Erosion can wear down the blade surfaces, affecting their aerodynamic shape and performance.

 Vibrations: The churning effect can induce vibrations in the turbine rotor and other components. Excessive vibrations can cause mechanical stress and fatigue, leading to increased wear and potential failures.

 Loss of efficiency: The presence of liquid droplets in the steam reduces the effective energy transfer from the steam to the turbine blades. This can result in a decrease in overall turbine efficiency and power output.

 To mitigate the this effect and protect the turbine blades, several measures can be implemented:

 l Proper design of steam Turbine & blading to ensure proper expansion of steam in blades.Blade Design: Turbine blades can be designed to minimize the impact of churning. This can include using erosion-resistant materials, shaping the blades to minimize droplet impingement, and providing protective coatings.

 l Drainage Systems: Proper design and implementation of drainage systems within the turbine help remove condensed water and moisture effectively

 l Proper operation of the Turbine & maintaining steam parameters as per design

 l To mitigate the moisture content in steam and its negative consequences, steam turbines are equipped with various mechanisms and components, including steam separators, moisture separators, and steam dryers. These devices help remove or reduce the moisture content in the steam before it enters the turbine, ensuring better steam quality and minimizing the chances of churning.

 Proper design, operation, and maintenance practices, such as regular inspection and cleaning of turbine components, are essential to prevent or minimize the churning effect and maintain optimal turbine performance and longevity.

10-Difference between fixed nozzle and Variable nozzle de-super heating

  

 De-superheating is the process of reducing the temperature of superheated steam. This is typically achieved by injecting a cooling medium, such as water, into the steam flow. The nozzles used in the desuperheating process can be classified as either variable nozzle or fixed nozzle de-superheaters. Here's

 The differences between these two types are:

Sl No.	Variable nozzle de-super heater	Fixed nozzle de-super heater
1	Variable nozzle desuperheating systems have adjustable nozzles that allow for controlling the flow rate of the cooling medium injected into the steam flow.	Fixed nozzle desuperheating systems have non-adjustable nozzles, meaning the cooling water flow rate and the degree of desuperheating are fixed
2	The nozzle opening can be adjusted to vary the amount of cooling water injected, thereby controlling the degree of desuperheating and achieving the desired steam temperature.	Separate control valve is required to adjust the water flow
3	More flexibility in adjusting the cooling water flow rate and achieving precise temperature control.	Not much accuracy in temperature control
4	Variable nozzle desuperheating systems are often used in applications that require tight temperature control,	USed where there is much tolerance in temperature control, Ex: In process industries They are commonly used in applications where a constant degree of desuperheating is sufficient, such as in industrial processes with steady steam loads or in small-scale power plants.
5	Complex design	Simple design
6	More costlier than fixed nozzle de-super heaters	Less costlier
7	Little bit complicated operation	Simple operation
8	Can be used for variable inlet flow & temperature	Used only for fixed flow & temperature
9	Size of nozzle is variable	Size of nozzle is fixed
10	Maintenance is difficult & costlier	Maintenance is simple & cheaper

 The choice between a variable nozzle and fixed nozzle desuperheater depends on factors such as the required temperature control accuracy, steam flow variability, plant operating conditions, and budget considerations. Variable nozzle desuperheaters are often preferred in applications where precise temperature control and flexibility are crucial, while fixed nozzle desuperheaters can be suitable for applications with relatively stable operating conditions and lower cost requirements.

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Why pressure reducing of steam is being done before de-super heating?

 Following advantages we can have, if pressure reducing is done before de-super heating

1.  Reducing the pressure before de-super heating helps in controlling the steam temperature with great accuracy.High-pressure steam entering the de-superheating station can be challenging to control accurately due to its high energy content. By reducing the pressure, the energy content decreases, allowing for better control of the de-superheating process and ensuring that the desired steam temperature is achieved.
2.  Heat transfer between water & steam is more better at lower pressure
3.  Helps is protecting the down stream equipment if desuper heating is done at lower pressure since there will not be no any much chances of low or high temperature steam entry into the Turbine or process.
4.  Erosion of down stream pipe lines can be minimized due to high pressure & high velocity steam
5.  Cost of high pressure lines can be reduced.
6.  Total head required for de-superheating water will be reduced, thereby reducing feed pump pumping power.
7.  Related cost of control valves & pipe lines will be reduced
8.  Damage to the de-super heating equipment can be reduced by avoiding thermal shock by avoiding direct mixing of high pressure steam and high pressure water
9.  Pressure reduction before the de-superheating station helps maintain safe operating condition.High-pressure steam carries a greater risk of causing damage or injury in the event of a malfunction or sudden pressure surge. By reducing the pressure beforehand, the risk of high-pressure steam reaching the de-superheating station is mitigated, enhancing overall system safety.
10.  Pressure reduction can also contribute to overall system efficiency. Lowering the pressure before the de-superheating station helps control the temperature more effectively, resulting in more efficient heat transfer and reduced energy consumption.
11. Reducing the pressure before de super heating will also helps in reducing the temperature of steam, which helps in reduction of water quantity required for desuper heating

 

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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.	Interlock	Significance
1	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
2	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
3	FD fans trip-Fuel feeding system trip	To avoid jamming of fuel feeding system & grate
4	High furnace draught-FD & SA fans trip	To avoid furnace explosion
5	Low furnace draught-ID fans trip	To avoid explosion of ESP & related ducts to vacuum pressure
6	High main steam pressure-Boiler trips (FD & fuel feeding system)	To avoid failure of pressure parts due to high steam pressure
7	High main steam temperature-Boiler trips (FD & fuel feeding system)	To avoid failure of pressure parts due to high steam temperature
8	PA fan trips- Fuel feeding system trips	To avoid jamming of fuel feeding system
9	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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