This reads like the live steam pressure is reduced due to the new heat source. This may indecate a sub-optimal design of the HRSG with respect to the given turbine, i.e. the HRSG produces less steam than the turbine consumes. To keep the extraction flow constant you have two options: a) decrease back pressure at the low pressure side or b) increase pressure at the turbine extraction position by installing a pressure maintenace valve downstream the extraction before entering the LPT. The solution you chose strongly depends on your specific system and is affected by constructive and operational constraints.

Hope this helps, Friedrich

By reducing the condenser presure.

In  a combined cycle system, the steam power system uses the low temperature heat source, so there is no regenerative extracted steam generally.  However, you can extract the steam from the turbine ( for example,  set a hole at the pipe between IP and LP) to creat a CHP system

thank you for your answers.

the capacity of cooling tower is constant, so we can not reduce the condense pressure.

we can extract steam easily, but we want to know that how can use this steam efficiently? the CHP system is a good idea, but where do use this heat?

according to almost intermediate temperature of the weather (Iran climate), using this heat for household heating is not efficiently.

is it a good idea to use an other litle scale rankine cycle and use extracted steam to feed it? in this case, we need an other cooling tower too.

By employing regenerative cycle and reducing condensor pressure