This invention relates to a heat exchanger comprising a bundle of substantially parallel heat exchanger tubes for use in a primarily stationary fluidized bed, in which solid particles are put into a fluidized condition by supplying a fluid or gas stream, for heating or cooling the fluidized solids and the medium in the tubes.

In a stationary or bubble-forming fluidized bed, solid particles are put into a fluidized condition by supplying a fluid or gas stream, in particular fluidizing air, in which a close contact occurs between the fluidized material and the fluidizing medium. The fluidizing air generally is introduced into the solids bed from below through a gas distributor, in order to achieve a uniform fluidization. In the fluidized bed, a treatment of the fluidized material then is effected by heat and/or mass transfer, before the same is withdrawn from the fluidized bed. The heat or mass transfer is influenced by the bubble size of the fluidizing air introduced into the fluidized bed.

For heat treatment of the solid particles in the fluidized bed, it is also known to provide a shell-and-tube heat exchanger in the same, through which a heating or cooling medium is passed, in order to heat or cool the fluidized material. Usually, these tube bundles consist of few, relatively large heat exchanger tubes, in order to avoid clogging of the bundles. The heat exchanger tubes influence the flow of the fluidizing air in the fluidized bed.

It is the object of the present invention to optimize the heat transfer in a stationary fluidized bed.

In a heat exchanger as mentioned above, this object substantially is solved with the invention in that the horizontal clear tube spacings lie in the range from 10 to 30 mm, preferably 12 to 20 mm, and that the vertical clear tube spacings are 15 to 50 mm, preferably 20 to 30 mm. The diameter of the heat exchanger tubes should be about 15 to 50 mm, preferably between about 20 and 30 mm.

Surprisingly, it was found out that the use of such heat exchanger as compared to conventional heat exchangers with greater tube pitches and tube diameters involves a significant reduction of the bubble size of the fluidizing medium. Due to the smaller bubbles, a more uniform mixing of the fluidizing gas with the solids is obtained. As a result, the heat transfer in the system of fluidizing gas, solids, bundle, heating/cooling medium in the heat exchanger tubes is improved. In addition, the reduced implosion energy of the gas bubbles results in a reduction of the solid material discharged from the fluidized bed. As a result, negative dust cycles are reduced and the efficiency is increased. The solution in accordance with the invention also leads to a reduction of the size of the heat ex- changer. If the object of the process is the production of energy, the medium in the tubes is the primary product to be treated and will be heated (or cooled).

In accordance with a development of the invention it is proposed to connect, in particular weld the heat exchanger tubes in the bundle via sections extending substantially vertical to the heat transfer tubes. Because of the smaller gas bubbles, a higher frequency is measured in the heat exchanger, which might easily oscillate and thereby damage the heat exchanger tube bundle. This is prevented by welding the heat exchanger tubes in the bundle to sections. Due to the vertically arranged sections, the flow of the fluidizing medium is not substan- tially influenced either.

The heat exchanger tubes can be connected with the sections via holders, wherein the heat exchanger tubes preferably are held in recesses of the sections, in order to achieve a more stable attachment and reduce the width of the heat exchanger. In accordance with a development of the invention, the sections are connected with each other via the clampings, wherein the clampings in particular are welded to the holders and/or the sections. This results in a very stiff heat ex- changer tube bundle of relatively great weight, which the bed frequencies no longer can induce to oscillate.

As simple commercially available components for the heat exchanger tube bundle, round tubes can be used for the heat exchanger tubes and square sections can be used for the stiffening sections.

This invention also relates to a fluidized-bed reactor with a heat exchanger of the type of the invention as explained above. In such fluidized-bed reactor, in particular the two essential effects are achieved, according to which on the one hand the heat transfer is improved and as a result the heat exchanger can become smaller, and on the other hand the product efficiency can be increased by reducing the fluidized produced discharged as a result of the small bubble energy.

Further developments, advantages and possible applications can also be taken from the following description of an embodiment of the invention and the drawing. All features described and/or illustrated form the subject-matter of the invention per se or in any combination, independent of their inclusion in the claims or their back-reference.

In the drawing:

Fig. 1 shows a vertical section through a heat exchanger bundle of the invention, and Fig. 2 shows a partial top view of the heat exchanger bundle of the invention.

The heat exchanger in accordance with the invention includes a bundle 1 with heat exchanger tubes 2 extending substantially parallel to each other for use in a stationary fluidized bed. For heating or cooling the fluidized solids of the fluid- ized bed, the heat exchanger tubes 2 can be charged with a heating or cooling medium.

In the illustrated embodiment, the heat exchanger tubes 2 are arranged in several rows preferably offset with respect to each other.

The horizontal clear tube spacings Ah lie in the range from 10 to 30 mm, preferably 12 to 20 mm, and the vertical clear tube spacings Av are 15 to 50 mm, preferably 20 to 30 mm. The horizontal tube pitch (Th) and vertical tube pitch (Tv) as indicated in the drawing are the spacings of the longitudinal tube axes. They are obtained by determining the clear tube spacings and the tube diameters. The diameter of the heat exchanger tubes should be about 15 to 50 mm, preferably between about 20 and 30 mm.

The heat exchanger tubes 2 in the bundle 1 are clamped via holders 4 by means of square sections 3 extending substantially vertical to the heat transfer tubes 2. The clamping effect is obtained by the welding seams 5. The sections 3 include half-round recesses 6, into which the heat exchanger tubes 2 each are inserted with half their circumference. Adjacent sections 3 are connected with each other via clampings 7, which preferably are welded to the holders 4.

At their upper and lower ends, the sections 3 each are closed in a manner not shown here, so that no fluidizing air and no solids can pass through the same. List of Reference Numerals

1 bundle

2 heat exchanger tubes

3 sections

4 holder

5 welding points

6 recesses

7 clampings/spacers

A clear spacing D diameter T pitch