Feedwater heater drain valve

Introduction

Feedwater heater is a shell-tube heat exchanger used in power plant. Feedwater is heated and pressurized before it goes to steam drum. Steam from turbine goes through shell pass and transfers heat to feedwater in tube pass. Steam will condensate into water, which forms a level of condensate. The level is controlled to avoid blow-through of steam extraction line. Also, we should avoid liquid level rising too high to achieve maximum heat transfer from steam to feedwater.

So accurate level control is key to efficient operation of feedwater heater. Traditional level control by float/pneumatic/electric switch is high maintenance, bad reliability due to complex actuator, frequent movement, jamming and leakage problem.

Vapor-liquid two phase flow level control drain valve is breaking new product to replace the traditional level control valve. It is preferred by power plant clients due to novel design, advanced principle, self-regulating ability, small size, no moving parts, high reliability & safety, stable level control. Level fluctuation is no more than ±20mm when boiler duty varies greatly (100％～30％～10％ for units below 200MW, 100%～30% for units 300-600MW).

Application

Feedwater heater drain valve is used for the level control of various heat exchangers in power generation, oil, chemical, paper making, printing & dyeing, metallurgy industry, such as high & low pressure feedwater heater, gland steam condenser, heater for R/O water, heater for district heating network, flash tank, steam air heater, etc. In a word, any vessel that has vapor-liquid interface inside could use this to control the drain flow.

Working principle

Drain valve is based on fluid mechanics theory. It is new concept level regulator according to two phase flow characteristics. It consists of a signal pipe and regulator. Signal pipe is to send water level signal and transport steam for level control, while regulator is to control drain flow.

When water level inside heater declines, steam flow through signal pipe increases. The steam will suppress the water flow through orifice, and water level will rise up. When water level is high, steam flow through signal pipe decreases. Water flow through orifice will increase, and water level will drop.

Advantages

1. Wide application & adaptability. Suitable for heat exchanger for large unit with wide varying duty.
2. Stale level control. It could achieve continuous self-regulation under varying duty operation.
3. High safety & reliability. No mechanical moving parts, no electrical driving parts, no need external driving force.
4. Long service life. Made of stainless steel to withstand corrosion under high temperature.
5. No malfunction, no maintenance.
6. Easy installation.
7. Greatly reduce cavitation erosion and vibration of pipeline.

Technical

Working pressure: ≤ 10.0 MPa
Working temperature: ≤ 425℃
Steam consumption for adjustment: <0.5% of drain
Flow: max value in design
Signal pipe: based on our specification