1.4 Regenerative Feed Heating

Introduction

There is a large difference between super heated steam temperature, as supplied from boiler to turbine and the condenser temperature, as it leaves the condenser and is recycled to the boiler as a boiler feed water. Now to increase the condensate temperature, on its way back to the boiler and as a consequence to increase the thermal efficiency of the plant, the process of regenerative feed heating is introduced.

In this process small quantity of steam drawn at various stages of the turbine are allowed to pass through several feed heaters. Whereupon they condense in the process of either direct heat exchanger or indirect heat exchanger with the condensate being pumped to the boiler.

Method
Direct contact feed heating	Indirect contact feed heating
	Drain pump method
	All drains to Hot Well method
	Cascade method

 

Feed water heater:

A.      Close type heater => They are basically shell and tube type heat exchanger which operated at higher pressure then condenser because bleed steam is condensed on the shell side whereas feed water, acting like circulating cooling water in the condenser, is heated on the tube side (LP & HP Heater).

B.      Open type heater=>  It is one in which the feed water is heated by direct mixing with the bleed steam of turbine (De-aerator).

Terminal Temperature Difference (TTD) = saturation temperature of bleed steam - exit water temperature.

A HP Closed Feedwater Heater has three zones:

• Desuperheating zone.
• Condensing Zone.
• Drain cooling Zone.

Each zone is designed as a separate heat exchanger and heat transfer coefficients and pressure drops are evaluated separately.

Regenerative feed heating system

LP Heater	HP Heater