do you see gas savings in installing back pressure turbine instead of PRV

[vir07]

HI I am working on a project where PRV is currently taking 210 PSI steam and converting it to 10 PSI steam. This creates an energy loss
The customer is proposing taking existing 70 PSI steam from the exhaust end of an electricity-generating steam turbine to convert to 10 PSI steam instead with a new PRV.
What I’m unclear on: The 70-to-10 PSI steam PRV is expected to save 1400 MWh due to more steam being drawn through the turbine generator, increasing its output to the plant.
However, gas savings mentioned anywhere in the project documents even though it’s planned that the 210 PSI steam isn’t going to be used to make 10 PSI steam anymore. Are there actually no gas savings associated with this measure ?

 

[TBP]

I doubt that you'll see any measurable change at the boiler - the proposed changes are all downstream at the back pressure turbine and PRV stations. The big nugget will be the increased electrical power generation, then using the steam that made that possible again, in whatever process the 10 PSI steam supplies.

 

[MJCronin]

You should have a mass and energy balance model of your entire boiler and steam distribution system developed

By use and manipulation of this model these questions can be answered.

The model can be used to evaluate various plant configurations for major capital investments as well as maintenance changes

This is a relatively small investment for a large plant

http://swopnet.com/engr/stm/steam_dist_eff.html

https://onlinelibrary.wiley.com/doi/abs/10.1002/9781119033226.ch18

https://www.unido.org/sites/default/files/2017-11/SSO-Manual-Print-FINAL-20161109-One-Page-V2.pdf

MJCronin
Sr. Process Engineer

 

[crshears]

Another option:

https://www.thermoflow.com/products_overview.html

I do not work for Thermoflow and have no vested interest in the company, its software, or its personnel.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[pierreick]

Hi,
Consider this calculator (with examples) to support your work :

https://www4.eere.energy.gov/manufacturing/tech_deployment/amo_steam_tool/

Good luck
Pierre

 

[davefitz]

There will be more money generated by the sale of the additional electricty, so the economics of the plant will improve. It is feasible to further improve the electrical output by also passing the 70 psi steam thru a small backpressure turbine generator exhausting at 10 psi. Such small turbine generators can be automatically synched to the grid using the same technology used by Capstone gas turbines.

It is always true that expanding the steam isentropically across a turbine is more efficient than an isenthalpic drop across a pressure reducing valve, but there can be issues with excess liquid content of the exhaust steam. In general the exhaust should not be more than 10% lqiuid by weight to avoid erosion of the turbine blades.

In the upcoming "green " future, replacing pressure reducing valves with automatically synching turbines ( or pelton wheels) may become more popular, for all working fluids , but espescially for expandable gases.

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick