Steam Turbo-generators

[axx1]

Hi,

My company has recently discovered the potential benefits of replacing pressure reducing valves (PRV) on the steam line with steam turbo-generators. We approached a supplier to assess the potential for generating electricity in our steam system.

With the information we gave them, they gave us a summary of how much electricity we could produce. My company wants me to verify the figures that were presented to us.

Can anyone help me with the calculation to determine the energy available for conversion, given the inlet and outlet pressure and steam flowrate through the PRV.

Thanks.

 

[byrdj]

(h1-h2)*q

 

[GregLocock]

(h1-h2)*q*eta

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[BrianPetersen]

... and the "h" figures in the above are enthalpy from the steam tables that you can look up in a thermodynamics textbook.

 

[sacem1]

May I ask why do you need to reduce pressure in your steam line in such amount that cogenerating electrical energy is possible, why don't you start by reducing your steam temp and avoid using energy to create steam in an enviroment that, I assume, is not designed to generate electrical power as a main function and there fore is not efficient as it should be.

Just wondering, that's all.

regards

SACEM1

 

[TheTick]

But, sacem1, that would subvert the synergy of the value-added paradigm!

 

[axx1]

Sacem1,

Our boilers produce steam for the entire paper mill, which has many sub-sections eg. Pulping plant, belaching plant, paper machines, liquor recovery etc. Each subsection use steam at different pressures (and temperatures). That is why we distribute steam at a constant 15bar to all sections and have reducing stations to meet the particular requirements of that section.

Thanks.

 

[byrdj]

Are you aware that the steam turbine can have multiple extrations to provide the different header pressures. Several of those extractions can also be "controlled", that is the ST would throttle its valves to maintain the header pressure as usage varied (at the cost of changing electrical output)

 

[rmw]

Every paper mill I have ever been in used multiple steam turbines both power generation and mechanical drive types of turbines to drop steam pressure along the line from boiler pressure(s). The last I remember was steam boilers at 1800 psig dropping down through a power generation turbine to the 600 psig header with the mechanical drive turbines driving the paper machines operating at 600 psig exhausting at 150 and 15 psig. A myriad of smaller pumps used 150 psig steam and exhausted to the 15 psig header. The 15 psig steam was used in the drying rolls.

Parallel to this system were other electric power generating turbines operating as byrd has indicated with double and triple automatic extraction points to control the 600, 150 and 15 psig headers. Typically there is a least one electric generating turbine operating with extraction plus condensing in order to be able to generate power if the intermediate pressure systems have no demand.

As some mills converted to or installed newer electric drive type paper machines more steam was dropped only through pure power generation turbines, extracting at 150 and 15 psig. But the lowest pressure steam is still needed for paper roll drying.

axx1, where is this paper mill that hasn't implemented this type of technology yet?

rmw

 

[axx1]

rmw,

Thank you for the information - it has been a real eye opener! The paper mill where I work is in Gauteng, South Africa.

Are you able to name any of the paper mills that implement this technology? The company I work for has paper mills around the world so perhaps I could get assistance from our international head office.

axx1

 

[byrdj]

Ever paper mill in the US, whether it be preWWII or new, I have ever been in had a steam turbine generator. But then I would have no reason to go if they didn't

 

[rmw]

Axx1,

If you can state in direct terms or discreet terms which company I will state the plants that I have experience with that are similarly structured. They represent a large variety of well known company names such as International Paper, Georgia Pacific, Nekoosa, Domtar, Weyerhauser, Western Kraft, Continental Can, to name a few, and numerous smaller independent mills.

rmw

And PS: please don't double post. I just clicked into the 'twin' thread and wondered where the heck my post was. I owe an apology to Dave.

 

[axx1]

rmw,

Firstly, my apologies for the double post - I am a chemical engineer and naturally posted it there first. I then posted it here because I wasn't sure if mechanical engineers like yourself would see it. But sorry for any trouble caused.

The company I work for is Sappi. Can I assume that your company is involved in these steam turbine systems?

byrdj,
Do you work for a company involved in these systems? If so, can you give me the name?

Thanks.

axx1

 

[byrdj]

I worked for a company that performs maintenance on ST-Gs (mainly General Electric). These were normally relatively large units of 50 to 100MWs In the US, Dresser Rand makes some very small (HorsePower rated steam turbines)

One importaint thing to consider for a retro fit would be the mass flow rate capability of exisitng boiler.

to increase the electrical power generated from the amount just from expanding the plant process steam, usually extra flow is taking to a condensor

 

[rmw]

axx1,

I started to answer no, but I should really say not too much. We have a few units in pulp and paper applications but most of what I said above comes from experience from former lifetimes.

I would suggest that you google the word tappi which is the abbreviation for Technical Association of the Pulp and Paper Industry. It is worldwide and may be available in SA.

I don't know how many resources that they have for power boilers/turbines as I found that the power plant in a paper mill was always viewed as a necessary nusiance. They needed it to burn up all their bark and mill waste, as well as to convert the chemicals (Kraft process) used in the pulping process but operating a power plant wasn't part of the core business which was making paper. They did like the steam for drying paper however, just that they didn't like having to operate the plant that made it.

If you join or otherwise get access to their site there may be some resources there for you. Otherwise, you might consult with your major turbine manufactureres or even boiler manufacturers to see if they have any descriptive literature for their units used in those applications.

rmw