Question about the Ramping-up procedure for a steam boiler

In summary: not because the water level drops below a certain point but because the feedwater can't keep up with the steam demand.
  • #1
Chandrakanth_balusa
25
2
Hello Experts,

I have a question regarding the operation of a steam boiler.
if the load is increased on the turbine generator set of a steam power plant, i learned that the fuel injection to the boiler has to be increased to serve the additional load. so my question is, do we also have to increase the feed water flow to the boiler? I have different answers from different people.
one of those was the water supply to the boiler is always maintained constant at constant pressure, the only difference we see is that the amount of steam generated in the boiler varies with the fuel input and the rest of the water keep circulating from the boiler to the feedwater tank.

may I know if how exactly does it work in the real scenario? is the pressure before and after the boiler is same? also is the mass flow of water to the boiler is always constant?

how can we estimate the time taken to ramp up the boiler from one load to another?

thank you in advance

yours sincerely

Chandrakanth Balusa
 
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  • #2
If the boiler water is a closed circulation system then no external water makeup will be required.

The rate at which water circulates from the boiler to the turbine, condenser and feed-water tank, then back into the boiler, will be proportional to the rate of steam generation.
The mass flow of water into the boiler must equal the mass flow of steam generated.
More fuel, will generate more steam, will need more boiler water injection.

The boiler pressure can remain the same, but may be changed for better economy.
More details of the particular system are needed before a better answer can be given.
 
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  • #3
Chandrakanth_balusa said:
how can we estimate the time taken to ramp up the boiler from one load to another?
  1. First find out the kind of boiler, once-through, or drum. Superheat sections or not? Reheat sections or not?
  2. Then you need to know the amount of energy stored in the boiler steel, and in the water/steam in the boiler.
  3. Then the dynamics of the fuel system. How rapidly can fuel flow be changed? Air flow and fuel flow need to maintain a rough balance, so the rate of change of air flow also matters.
  4. Then you need to know the operating limits. How high? How low is drum level allowed to go? How high/low the temperatures in the furnace and superheater walls?
  5. Then you need the control system details. Most likely, the boiler controls are of the "load follow" type. The turbine speed governor opens the valves to allow more steam. That makes pressure drop and drum level to swell. A control loop varies fuel flow to hold pressure constant. Another loop varies feedwater flow to hold drum level contant. Another loop changes burner tilt to hold temperatures constant.
The best source for all that information is the manufacturer/designer of the boiler control system. Without that, you'll have to make your own dynamic models, or you could run tests and measure the transient responses.

In the title you said ramping-up, but in the body you are talking about change of load. Ramp-up usually refers to starting a cold boiler, not change in load. During cold startup, rate of change of temperatures are the most limiting factors.
 
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  • #4
I have quite a bit of experience in the operation of boilers. I worked for a asset management company that operated and maintained boilers for factories. I don't have much experience with power generation though. This is what I know.

With a normal packaged boiler:
The factory activates more of their machines- more steam is being drawn through the steam lines from the boiler. Steam is produced from water that has entered the boiler, therefore the boiler's water level starts to drop. More feedwater must enter the boiler to make up for the steam that is leaving. The water entering the boiler must always equal the steam leaving the boiler on a tonne for tonne basis. Actually, to be honest, the amount of water entering the boiler will always be more over a given time period. The reason for this is that a certain amount of water is being dumped from the bottom of the boiler periodically to get rid of dissolved solids that get concentrated in the boiler water over time.
Bottom line: If more steam is being drawn from a boiler then more feedwater must be pumped into the boiler. If you fail to do so the water level in the boiler will drop and you will have a very unsafe situation. If you want to destroy a boiler and the surrounding countryside, let the water level inside it drop below the safe working levels. I'm pretty sure that more boilers fail due to lack of water than from overpressure.

Under no circumstances will water be allowed to circulate between the feedwater tank and the boiler directly. The feedwater tank is a storage tank that collects water for use inside the boiler. In a good system a lot of that water will be coming back from the process and some of the water will be coming from municipal supply. So a combination of municipal water and condensate enters the hotwell tank (feedwater tank). That water is then pumped from the hotwell tank by your feedwater pumps. The feedwater pumps pump directly into the boiler. Water must be pumped into the boiler at a pressure slighly higher than the boiler pressure, otherwise the water will not move into the boiler. Yes, the pressure before and after the boiler is almost the same.

Now to answer your other question regarding fuel. Yes, if you draw more steam from a boiler you will have to increase the fuel supply. With a packaged boiler the increase in steam draw will result in the pressure dropping inside the boiler. This drop in pressure is detected by a transducer which then signals the Induced draught fan to speed up so that more air gets drawn through the flue. The Forced draught fan then picks up that the induced draught fan is pulling more air and it speeds up as well. The fuel delivery system is linked directly with the forced draught fan and it speeds up as well. Thus more air and fuel gets delivered to the boiler so that more energy get's liberated into the water and steam supply can be maintained at the correct pressure.

With a power generation boiler things are similar. They have economizers and superheaters and the water is a lot purer than for packaged boilers, but the basic idea stays the same. Power station boilers are often water tube instead of fire tube as well because the pressures are much higher, but once again, the basic idea stays the same.

If I remember I'm going to add in some diagrams tonight. Hopefully that will make things more clear.

I hope this has made sense. My experience is with these boilers:
1563963657934.png
 
Last edited:
  • #5
Baluncore said:
If the boiler water is a closed circulation system then no external water makeup will be required.

The rate at which water circulates from the boiler to the turbine, condenser and feed-water tank, then back into the boiler, will be proportional to the rate of steam generation.
The mass flow of water into the boiler must equal the mass flow of steam generated.
More fuel, will generate more steam, will need more boiler water injection.

The boiler pressure can remain the same, but may be changed for better economy.
More details of the particular system are needed before a better answer can be given.
Dear Mr. Baluncore,

thank you so much for your valuable information. few of my doubts are cleared
Hope i will come back to you again if i raise any doubt.

kind regards
Chandrakanth Balusa
 
  • #6
anorlunda said:
  1. First find out the kind of boiler, once-through, or drum. Superheat sections or not? Reheat sections or not?
  2. Then you need to know the amount of energy stored in the boiler steel, and in the water/steam in the boiler.
  3. Then the dynamics of the fuel system. How rapidly can fuel flow be changed? Air flow and fuel flow need to maintain a rough balance, so the rate of change of air flow also matters.
  4. Then you need to know the operating limits. How high? How low is drum level allowed to go? How high/low the temperatures in the furnace and superheater walls?
  5. Then you need the control system details. Most likely, the boiler controls are of the "load follow" type. The turbine speed governor opens the valves to allow more steam. That makes pressure drop and drum level to swell. A control loop varies fuel flow to hold pressure constant. Another loop varies feedwater flow to hold drum level contant. Another loop changes burner tilt to hold temperatures constant.
The best source for all that information is the manufacturer/designer of the boiler control system. Without that, you'll have to make your own dynamic models, or you could run tests and measure the transient responses.

In the title you said ramping-up, but in the body you are talking about change of load. Ramp-up usually refers to starting a cold boiler, not change in load. During cold startup, rate of change of temperatures are the most limiting factors.

Dear Mr.Anorlunda,

currently my thesis is just a research and so i don't have any details from the manufacturer. But, I am focusing more on the boilers used in pulp mills. so most probably the boilers used there are once through recovery or bark boilers. and yeah I was wrong about the ramping up time. thank you for clearing my confusion.

could you suggest me some software or programme apart from MATLAB to simulate the power plant_

thanks and regards

Chandrakanth Balusa
 
  • #7
Joe591 said:
I have quite a bit of experience in the operation of boilers. I worked for a asset management company that operated and maintained boilers for factories. I don't have much experience with power generation though. This is what I know.

With a normal packaged boiler:
The factory activates more of their machines- more steam is being drawn through the steam lines from the boiler. Steam is produced from water that has entered the boiler, therefore the boiler's water level starts to drop. More feedwater must enter the boiler to make up for the steam that is leaving. The water entering the boiler must always equal the steam leaving the boiler on a tonne for tonne basis. Actually, to be honest, the amount of water entering the boiler will always be more over a given time period. The reason for this is that a certain amount of water is being dumped from the bottom of the boiler periodically to get rid of dissolved solids that get concentrated in the boiler water over time.
Bottom line: If more steam is being drawn from a boiler then more feedwater must be pumped into the boiler. If you fail to do so the water level in the boiler will drop and you will have a very unsafe situation. If you want to destroy a boiler and the surrounding countryside, let the water level inside it drop below the safe working levels. I'm pretty sure that more boilers fail due to lack of water than from overpressure.

Under no circumstances will water be allowed to circulate between the feedwater tank and the boiler directly. The feedwater tank is a storage tank that collects water for use inside the boiler. In a good system a lot of that water will be coming back from the process and some of the water will be coming from municipal supply. So a combination of municipal water and condensate enters the hotwell tank (feedwater tank). That water is then pumped from the hotwell tank by your feedwater pumps. The feedwater pumps pump directly into the boiler. Water must be pumped into the boiler at a pressure slighly higher than the boiler pressure, otherwise the water will not move into the boiler. Yes, the pressure before and after the boiler is almost the same.

Now to answer your other question regarding fuel. Yes, if you draw more steam from a boiler you will have to increase the fuel supply. With a packaged boiler the increase in steam draw will result in the pressure dropping inside the boiler. This drop in pressure is detected by a transducer which then signals the Induced draught fan to speed up so that more air gets drawn through the flue. The Forced draught fan then picks up that the induced draught fan is pulling more air and it speeds up as well. The fuel delivery system is linked directly with the forced draught fan and it speeds up as well. Thus more air and fuel gets delivered to the boiler so that more energy get's liberated into the water and steam supply can be maintained at the correct pressure.

With a power generation boiler things are similar. They have economizers and superheaters and the water is a lot purer than for packaged boilers, but the basic idea stays the same. Power station boilers are often water tube instead of fire tube as well because the pressures are much higher, but once again, the basic idea stays the same.

If I remember I'm going to add in some diagrams tonight. Hopefully that will make things more clear.

I hope this has made sense. My experience is with these boilers:View attachment 247052
Dear Mr.Joe

thank you for your response towards my question.
so i am a bit more clear now with the circulation of feedwater with your answer. thanks for sharing your experience. this have helped me for sure!
Hope I can ask you another doubts if have any.

regards

Chandrakanth Balusa
 
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  • #8
Simulink is a software tool often used for physical models.

I did a search on "public domain boiler simulations." Here are some of the results.

http://www.ibpsa.org/proceedings/BS2009/BS09_0732_739.pdf
https://sourceforge.net/directory/?q=interactive simulations
https://sourceforge.net/directory/?q=power boiler simulator
But you still need cooperation from industry. Any simulation model needs V&V (verification and validation). Validation means checking to see if the model includes the features necessary to accomplish the goal. Verification means comparing results with data from independent sources to assure that the simulation is done correctly. Without V&V, you may create a simulation that everyone else ignores.

In most cases, industry is glad to cooperate with graduate students and to provide assistance. It is one way to recruit promising future employees. They may even allow you access to simulation models they already have that have V&V. You should reach out to them. Your professors may be able to help.
 
  • #9
anorlunda said:
I did a search on "public domain boiler simulations." Here are some of the results.
thank you Mr.Anorlunda,
anorlunda said:
In most cases, industry is glad to cooperate with graduate students and to provide assistance. It is one way to recruit promising future employees. They may even allow you access to simulation models they already have that have V&V. You should reach out to them. Your professors may be able to help.
yes this is a good thought, i do know few mills where I have been before. hope it works out this way.
Ill check the softwares you recommended.

thanks and regards

Chandrakanth Balusa
 
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Related to Question about the Ramping-up procedure for a steam boiler

1. What is the purpose of the ramping-up procedure for a steam boiler?

The ramping-up procedure for a steam boiler is designed to gradually increase the temperature and pressure of the boiler in order to prevent sudden changes that could damage the equipment or cause safety hazards.

2. How is the ramping-up procedure performed?

The ramping-up procedure is typically performed by gradually increasing the fuel and air flow to the boiler, while monitoring the temperature and pressure levels. This can be done manually or through an automated control system.

3. Why is it important to follow the ramping-up procedure?

Following the ramping-up procedure is crucial for the safe and efficient operation of a steam boiler. Sudden changes in temperature and pressure can cause stress on the boiler and its components, leading to potential malfunctions or even explosions.

4. How long does the ramping-up procedure usually take?

The duration of the ramping-up procedure can vary depending on the size and type of the boiler, as well as the desired temperature and pressure levels. In general, it can take anywhere from 30 minutes to several hours.

5. Are there any risks associated with the ramping-up procedure?

While the ramping-up procedure is necessary for the safe operation of a steam boiler, there are some potential risks involved. These include the risk of overloading the boiler, as well as the risk of human error if the procedure is not followed correctly. It is important to have trained personnel and proper safety protocols in place when performing the ramping-up procedure.

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