Steam & Power Forum RSS

360 MW Techanical specfication for thermal power plant - By: John [788]

Wed, 1 Feb 2012 13:39:00 -0300

Dear sir,

I want Technical specification of 360 MW thermal details , Anybody have the materials kindly forwarded the same .

Re: 5D radiuis bends in the steam lines - By: N.Ramani [965]

Wed, 1 Feb 2012 08:16:00 -0300

As indicated by others in high energy systems like Main steam to turbine the radius of bends are between 3D and 5D.and made as per spec to save pressure loss. In other systems it is 1.5D or 1D. where the cost benefits may not justify longer bends.Smaller radius make the systems more flexible though there is an increase in pressure drops.It also helps in being elective in narrow space for routing the systems.It depends on case to case basis keeping the cost in mind.

Re: KW cost calculation - By: Pardha [1157]

Tue, 31 Jan 2012 06:58:00 -0300

The price 0.04$/K WHr includes fuel cost, Salaries to the engineers and technicians, power consumed by the equipments, profit, etc.,

Out this 0.04$/K WHr what fraction amount does fuel cost..?? If you know this value one can calcuate the new cost per KWHr generated for an increase in 10% of boiler efficiency case..

Regards
Pardha

Re: 5D radiuis bends in the steam lines - By: Pardha [1157]

Tue, 31 Jan 2012 00:50:00 -0300

Thanks Rick...

Re: 5D radiuis bends in the steam lines - By: Rick [195]

Mon, 30 Jan 2012 09:13:00 -0300

They would be appropriate to use from the perspective of minimizing pressure drop. However, they are not standard fittings and would have to be special ordered which would drive up both the cost and the delivery time.

Re: 5D radiuis bends in the steam lines - By: Pardha [1157]

Sun, 29 Jan 2012 23:58:00 -0300

Thanks Rick..

My second question in simple terms if we can decrease the pressure drop across the system then why dont we use these 5D bends in other systems or lines for example condensate or feedwater pipelines.

Re: 5D radiuis bends in the steam lines - By: Rick [195]

Sat, 28 Jan 2012 16:33:00 -0300

Answer to the first question is most likely yes.

I dont understand your second question.

5D radiuis bends in the steam lines - By: Pardha [1157]

Tue, 24 Jan 2012 07:03:00 -0300

Dear all,

I have obsereved in the customer specification asking for 5D bend where ever possible in the steam lines. What is the reason for using 5D radius bends. Is this only to decrease pressure drop in the bends.

Second question is because 5D bends save energy by decreasing the pressure drop in the bends, we dont use them in regular piping applications. We only go for LR elbows over SR elbows.

Thanks in advance....

Re: desuperheater control - By: Glencannon [28]

Thu, 19 Jan 2012 01:51:00 -0300

What process are you supplying that has such wide swings?

Re: desuperheater control - By: Jim Watts [764]

Sun, 15 Jan 2012 06:08:00 -0300

On rereading it , the last sentance should say the same amount of heat is sent to the process as there is actually more steam flow when desuperheated , it is just holding slightly less heat per pound but has more pounds.

Re: desuperheater control - By: Jim Watts [764]

Sun, 15 Jan 2012 06:01:00 -0300

The steam being used by the process is preferably saturated as this gives the best use of heat exchanger surface area.
Your set point of 350 F is only 12 degrees above saturation so when you say all the way down it is not a large change unless it also swings up towards the 650 F it is starting at. If you had a boiler designed for this job there would be no superheat. The only reason for your setpoint is possibly to reduce condensation along the line by taking any heat loss as temperature change, this reduces the possiblity of water hammer and reduces condensate handling by steam traps and the process heaters. However if you have difficulty maintaining a steady temperature there is more hazard from thermal cycling stress in the piping close to the desuperheater particularly at the welds. You may be better of reducing your setpoint closer to saturation and using a flow ratio cascade loop to control the water flow to the desuperheater. It is better to accept swings into wet steam which do not change the temperature provided water hammer does not occur.Just check all piping low poits are properly draining with servicable steam traps.

I do not know where the costs of desuperheating are supposed to be, as the boiler heat is delivered to the steam if it doesnt go up the stack and when desuperheated the sensible heat is converted to latent heat by making extra steam out of the spray water. The same amount of fuel is used and the same amount of water is boiled and the same amount of steam is sent to the process.

.

Re: desuperheater control - By: Barnstable1197 [365]

Sat, 14 Jan 2012 18:44:00 -0300

I dont believe the cost of desuperheating has been figured in. Its being done with boiler feed water and high pressure steam.

Re: desuperheater control - By: Rick [195]

Sat, 14 Jan 2012 12:28:00 -0300

How much is all this desuperheating costing you?

desuperheater control - By: barnstable1197 [365]

Fri, 13 Jan 2012 19:59:00 -0300

I operate a powerhouse in a process facility that has recently taking our backpressure turbine off line. While on line we didnt use the in desuperheater much. Now that the turbine is off line temp has to be reduced from 650 to 350 @100psi. The control points for the desuperheater are to close to the desuperheater causing wild fluctuations in temp at the end user. Sometimes the steam temp goes all the way down to saturation temp at the end user for extended periodsseveral hours at a time. What would be my major concerns here? Were trying to run leaving some superheat but with large load changes sometimes this is difficult.

Re: Reducing boiler pressure - By: Jim Watts [764]

Thu, 12 Jan 2012 08:46:00 -0300

From a thermodynamic point of view I have no doubt that the electricity being imported costs more to make than your back pressure turbine can produce it.
However some supply contracts require a take or pay provision to ensure load factor is above say 70 percent.
This makes the quirk that imported electricity is free until the load factor is reached.
As you point out such a wide generation range of 0.5 - 6MW it must be combining with process load swings and producing such low load factors that free electricity is available often enough to warrant shutting the turbine down.
This is a shame on the contract as, if the generator was treated as solar or wind, the supply utility would buy its output at a price where everyone would win.

Re: Reducing boiler pressure - By: barnstable1197 [365]

Thu, 12 Jan 2012 00:33:00 -0300

Thanks. The boiler pressure reduction didnt force the turbine off, it was just the opposite, management has decided it is more cost effective to purchase the .5 to 6 megawatts from the local utility than to produce it with the backpressure turbine. The turbine worked fine.

Re: Reducing boiler pressure - By: Jim Watts [764]

Wed, 11 Jan 2012 20:44:00 -0300

Reducing from 600psi to 300psi is a drastic measure and forces the turbine off.
It coincides with a reduction of two piping classes and is what you may do if you found you had the wrong steel in your system somehow.
The boiler circulation is not a problem as circulation is better with lower pressure due to the greater density difference with steam.
However a bottom drum desuperheater is a disrupter of circulation as there is a tendancy to reverse the circulation back up the downcomers. I would not use the desuperheater at low loads, and never if there is no reason to.

The boiler is not more efficient by desuperheating.
The pressure reduction has already reduced wall temperatures and superheater inlet temperatures and probably flue gas temps so efficiency has increased from that.

If the safety valves have not been reset to a lower pressure, there is a hazard if steam flow is blocked as the time to reach blow off pressure allows the superheater to overheat. Also the higher differential accross feedwater control valves will cause problems at low load.

Reducing boiler pressure - By: Barnstable1197 [365]

Wed, 11 Jan 2012 19:29:00 -0300

I posted earlier about reducing boiler pressure and got some good responses but wanted a little more info. The 600 psi boiler we reduced to 300 operates between 50 and 180 K lbs of steam an hour, even at loads of 50K lbs steam an hour there might be concerns with flow and potential hot spots in the boiler? There are no plans to remove the superheater. This boiler is also equipped with a mud drum desuperheaterattemperator that currently isnt doing anything as its purpose was to keep steam temp @750 for the turbine. In the current setup300psi, should I be trying to desup the steam here down to possibly 450 degrees? I would think this should help with boiler performance.

Re: Can i convert a 150hp Cleaver brooks to Run at 15psi??? - By: Glencannon [28]

Tue, 10 Jan 2012 23:45:00 -0300

Strictly speaking there are two types of pressure when you are talking about licencing. Anything 15 psi and higher is considered high pressure for licencing pruposes.

In Canada the rating on a steam plant is based on heating surface area and whether the boiler is low or high pressure. The plant is question is still a high pressure plant therefore would need a licenced operator in Canada.

Re: reducing boiler pressure - By: Glencannon [28]

Tue, 10 Jan 2012 23:37:00 -0300

I agree about the circulation problems in the water walls but since he would be taking the turbine out of the equation it would be possible to remove the superheater as well. If he is generating 300 # steam and he does not reduce the pressure untill the steam gets close to the end user he will have lots of superheat in the steam if he needs it due to the fact that you do not lose enthalpy when you throttle.

If the load is kept high enough there would be enough circulation to keep the water walls safe. That could be a problem with variable loads though. Some place to sink heat might be necessary such as a condensor that would put an artificial load on the boiler when there is no demand thus keeping the boiler load high.

The only real advantage I can see would be reduced fuel consumption but that might be offset by the added cost of power he would no longer generate himself by shutting down the turbine.The total cost of doing this would have to be studied very carefully looking at everything, not just what management wants to see.