Heat Pipe Air Preheater

Project Title

Design, Development & Demonstration of a 1.0 MW Heat Pipe Air Preheater

(B YH 88 977 RD 48)

Objective                           

To gain hands-on experience on the operation of a heat pipe air preheater

Project Description

A 1.0 MW heat pipe air preheater was developed and successfully tested on the oil-fired test facility at BHEL/Ranipet. The design of the air heater as a counter flow heat exchanger is based on 4 m long, 37 mm diameter internally grooved, integrally finned low-carbon steel heat pipes. Water is the working fluid. The heat pipe has an extra-unfinned length of 5% on the condenser side to accommodate the noncondensible gases produced during operation. BHEL/R&D evolved the designs while the manufacturing drawings as per standards were prepared by BHEL/Ranipet to suit the test track at Ranipet. The heat pipes were procured from M/s Fujikura, Japan as per our design and the manufacturing and assembly of the air preheater was carried out at BHEL/R&D. The unit uses 200 nos. of the heat pipes and is of overall size 4200 x 1700 x 650 mm. The equipment was laid at 7⁰ inclination to the horizontal and integrated with the test track with upstream/downstream ducts for flow stabilization.

The Heat Pipe Air Preheater
       

     Adequate instrumentation for the measurement of flow rate and temperatures is provided. Four calibrated venturi meters on gas/air side measured the flow rate while a peizoring arrangement measured the gas/air side pressure drop. The gas/air temperature is measured with 15 nos. of 28 SWG chromel-alumel thermocouples fitted in the stream. The heat pipe metal temperature on the evaporator side is also measured with a chromel-alumel thermocouple. The measured variables are:1) the gas/air flow rates, 2) the inlet/outlet gas/air temperatures, 3) the gas/air side pressure drop and 4) heat pipe metal temperature.

    The hot gases were generated for the experiments by an oil-fired combustion chamber located in the open circuit test track. The combustion nozzle has a small blower attached for mixing and distributing the gases. The hot gas flows over the evaporator sections of the heat pipes while the condenser sections receive a blast of cold air before entering the combustion chamber.

Heat Pipe Air Preheater under Integration with Test Track  

The air preheater was successfully tested at a heat pipe operating temperature of less than 200 ⁰C. The duty handled by the unit was 0.88 MW at an air flow rate of 17 kg/sec. The prototype testing under the project provided BHEL/Ranipet engineers an opportunity to gain adequate experience in the operation of heat pipe air preheaters.