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FLUIDIZED BED HEAT EXCHANGER WITH CONTROLLED INTERNAL CIRCULATION

Objective

THE MAIN AIM OF THE PROJECT IS TO STUDY HEAT EXCHANGE INDUCED BY INTERNAL CIRCULATION OF SOLIDS AND TO TEST THE FLEXIBILITY OF THE EXCHANGER RESULTING FROM LINKING THE EXCHANGE CHAMBER TO THE FEED CHAMBER BY MEANS OF AN AERATED V-VALVE, WHILE TAKING ACCOUNT OF THE RESTRICTIONS IN USE INHERENT IN CIRCULATING BEDS.
SINCE THE MAIN ADVANTAGE OF THE PROPOSED FLUIDIZED HEAT EXCHANGER IS ITS FLEXIBILITY OF USE, THE STUDY SHOULD CONCENTRATE MAINLY ON THE SOLID-THROUGHPUT REGULATOR VALVE. THIS WILL REQUIRE DETERMINING THE IDEAL GEOMETRY AND ASSESSING THE EFFECTS OF AERATION ON THE THROUGHPUT AND THE EXPECTED FLEXIBILITY, USING A COLD MOCK-UP. IN VIEW OF THE PROPOSED APPLICATION, THE SYSTEM SHOULD PERMIT A FLEXIBILITY OF 1 TO 3.
THE PROJECT SHOULD LEAD TO THE DESING OF A COMPACT AND FLEXIBLE HEAT EXCHANGER WHICH MAY BE TESTED IN USE WITH AN INDUSTRIAL BOILER.
When a fluidized bed is divided by a vertical wall into 2 communicating compartments of different overall porosities, a flow of solids is established between these 2 compartments.

It is known too that it is possible to control a solids flow between 2 fluidized bed reactors, thanks to a nonmechanical valveoperating with appropriate air injections.

The first phase of the work has been devoted to finding a valve aeration principle which could allow at least a 1 to 10 turndown ration in terms of solids flowrate going through. After some trials with a single point aeration device, showing no significant improvement compared to existing devices (which have a maximum turndown ratio of 1 to 4), a double aeration system has been studied and tested. The results obtained with this configuration were very promising. With a very small amount of air, it allows solids circulation through the valve with a turndown ration higher than 1 to 10. Moreover, the device is very well integrated, so that the overall size is small, compared to the fluidized bed compartments.

The second phase of the work began with the design and the building of a prototype heat exchanger, taking into account all the information obtained during the previous phase of the work. After a calibration period, in cold operating conditions, this heat exchanger has been installed below the cyclone dipleg of a 500 kW fluidized bed combustion unit for a series of tests in hot operating conditions. These tests have not been sucessful, because of size constraints due to the relative small size of the hot testrig and the operating range of the valve has not been reached. But it is sure that the design and aeration principle of the valve are correct.
THE NOVEL ASPECTS OF THE PROPOSED EXCHANGER ARE:

1. ITS INNOVATIVE GEOMETRY, COMPRISING TWO COMPARTMENTS, ONE OF WHICH CONTAINS A COMPACT BUNDLE OF TUBES. THIS GEOMETRY ENABLES THE SOLID CONTENTS TO BE CIRCULATED IN SUCH A WAY AS TO PROMOTE HEAT EXCHANGE ;
2. THE INTEGRATED NON-MECHANICAL REGULATOR VALVE WHICH PERMITS ADJUSTMENT OF THE RECUPERATION CAPACITY.

THE PHENOMENON OF AUTOCIRCULATION OF SOLIDS HAS ALREADY BEEN DEMONSTRATED, AND PRELIMINARY TESTS HAVE SHOWN THAT IT COULD BE USED TO IMPROVE HEAT EXCHANGE.
THE V-VALVE IS A WELL-KNOWN EXAMPLE OF NON-MECHANICAL VALVE WHICH WAS DEVELOPED IN A NON-AERATED VERSION IN CHINA. CERCHAR IS CURRENTLY DEVELOPING AN AERATED VERSION WHICH WILL BE INTEGRATED INTO THE GEOMETRY OF THE HEAT EXCHANGER.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

Centre d'Etudes et Recherches des Charbonnages de France (CERCHAR)
Address
33 Rue De La Baume
75008 Paris
France

Participants (1)

UNIVERSITE DE TECHNOLOGIE DE COMPIEGNE
France
Address

Compiegne