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Southern Company Services

Comment from Southern Company Services that is a followup to an earlier comment and email from EPA.
Note: The text refers to a drawing that cannot be converted to a Web-readable format.

Richard Chastain,
Research and Environmental Affairs

02/16/2000 09:30 AM
Subject: Output Based Emissions

Our engineering people have prepared the attached information in response to your recent questions. I hope this will be helpful. Please let me know if you would like anything more.

Richard H. Chastain
Research and Environmental Affairs
Southern Company Services, Inc.
Phone: (205) 257-6664
Fax: (205) 257-7294
RHChasta@southernco.com

In regards to the question about comment 6, we have prepared a sketch that is applicable to both the combustion turbine/steam turbine combined cycle power plant and the combustion turbine/steam turbine cogeneration power plant. That sketch is attached to this e-mail both as an MS-Word and as an AutoCAD file. The following is a short description related to this type of plant configuration:

Combined Cycle Power Plant (with and without Cogeneration) Combined cycle power plants in general terms consist of combustion turbine-generators (CTs) and steam turbine-generators (STs). In these configurations steam is sometimes taken from various places in the cycle for cogeneration purposes. The most common configuration for a modern combined cycle is two CTs and one ST although other combinations are also used (i.e. one CT/one ST, four CTs/one ST, etc.). Combined cycle plant configurations can be generally represented by the diagram labeled as Figure X.

From Figure X we can see that in this system fuel (heat input) is provided to the combustion turbine at A and this directly drives an electric generator. The hot exhaust gases from the CT generate steam at multiple pressure levels in the Heat Recovery Steam Generator (HRSG). Additional fuel can be provided to a burner mounted in the exhaust duct of the CT at B.

To compensate for the reduction of CT electrical output during hot weather it is sometimes possible to inject steam into the combustion turbine and this steam flow is shown at C. Any condensate associated with steam thus injected is lost from the cycle completely. Electric power to operate the CT/HRSG auxiliaries can come from the electric grid at D, the CT generator output at E, from other sources within the plant, or from a combination of these sources. Useful electric output from the CT generator is shown at F.

Steam from the HRSG at G and from additional HRSGs (if any) at H is used for various plant operational systems at I and is also provided to the steam turbine at J. The ST directly drives an electric generator. Additional plant operational systems will be provided with steam that is extracted from the steam turbine and this is shown at Q. If the plant also provides steam for cogeneration purposes this would be as shown at K and any house loads associated with this useful output is shown at L. Electric power to operate the ST auxiliaries can come from the electric grid at M, the CT generator output at N, from other sources within the plant, or from a combination of these sources. Useful electric output from the ST generator is shown at O.

Most of the condensate used by the steam turbine to generate power is returned to the cycle. Some of the condensate used for parasitic purposes or for useful steam loads will probably not be returned due to loss or contamination. Lost condensate must be replaced and the water treatment associated with this replacement will require electric and/or steam load and this is shown at P.

Calculation of the net steam and net electric output by a plant of this type is further complicated by the many voltage and pressure levels associated with the steam and electric parasitic loads. The general net output equations for the plant as a whole are represented as follows but it should be remembered that each item will probably require multiple measurements (represented by the "s" term in the equations). It should also be remembered that the number of emission points will be different from the number of electric generators and it will be extremely difficult to allocate net output to individual emission points.

Net plant steam output = K - L - (P * Y)
Net plant electric output (F + O) = (Es + Ds + Ms + Ns) - (Rs + Ss + Ts) - (P * Z) where:

In regards to the question about comment 9, we would like to see the following in the "Consensus Standards for Assuring Accuracy of Output Measurement Equipment" table on what was page 53:

As a footnote to the table please add the following: Other consensus based industry standards are also acceptable from the following organizations:

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