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.

 

[MJCronin]

axe...

Some comments:

- Give us the the inlet and outlet pressure and steam flowrate through the PRV.

- How many hours per year will the steam turbine be in use ?

- This type of equipment requires regular maintenance and, sometimes, an operator (in many US states). This strongly affects the ROI

- You might want to consult an engineering firm for a conceptual price/cost estimate. Frequently, there must be an upgrade to foundations, structures, piping and electrical systems with such an extensive change

-MJC

 

[dcasto]

you do understand that the turbo generator will remove energy from the steam, and therfore you will loose energy that the process formally used. SO, if the steam is used as a heating medium, you will have to make more steam.

There is no feee energy.

 

[axx1]

MJCronin,

Inlet P = 1300kPa (gauge)
Outlet P = 385kPa (gauge)
Ave q = 20 tph

Hours/yr = 8400


DCasto,

We currently have PRV's in the steam line where this energy is lost.

 

[chief]

Assuming an inlet pressure of 1300kPa of saturated steam, you will develop approx 3400 Kw, if you use a condensing type turbine.
You do not supply the available steam temperature,which if superheated will increase your power capability.
Saturated steam to a turbine will erode the turbine blades prematurely.

Offshore Engineering&Design

 

[dcasto]

There is absolutely no energy loss going through a PRV.

 

[MJCronin]

Chief...

Usually, a backpressure (not condensing)turbine with a controlled bypass is the most attractive in these installations... but your point about erosion due to saturated steam is well taken.

The addition of a turbine to an existing steam system is always difficult and having a steam system originally designed with some superheat is always best.

While a condensing turbine is certainly possible in such situations, you quickly get into more equipment maintenance requirements and cost of manpower that make any installation < ~ 5 MWe suspect.

-MJC

 

[MJCronin]

dcasto....

There is an extraction of mechanical energy that can be gained here while still using the latent heat of the exhaust steam

Wood and bagass plants have been doing this for nearly 100 years now.....

My MIT friends in Massachusetts have been earning a living providing packaged systems for many years.

See these links:

http://www.nestco1.com/energy_savings_turbine_over_prv.htm

http://www.nestco1.com/index.htm

http://www.nrel.gov/docs/fy02osti/31155.pdf

Please tell us where you are located and your final choice of equipment

-MJC

 

[dcasto]

there is energy available from the pressure yes, but that energy can also be used to heat something, its not free energy.

My thermodynamics teacher and friends have been doing this in refineries for 100 years and we balance our steam turbines with electric pumps to get a balance all the time. We turn off the steam turbines because we can make electricity cheaper or we need that steam energy more as heat than power.

 

[axx1]

dcasto,

I appreciate your point, but currently my country (South Africa) is going through a power supply crisis and is forcing industries to reduce electricity usage/dependance by 10%.

Although the energy can be used to heat something, an electricity reducing/generating initative carries more weight at the moment.

Thanks.

axx1

 

[dcasto]

so you will shift from electrict to fuel for power. Here is what I suggest then. Just replace electrict motors with steam turbine drives. They are plentiful in the used market. Typically, you have a spare pump, so you replace the motor with a turbine on it.