Cooling or heasting of free-flowing bulk materials in a water cooled or steam-heated tube-bundle heat exchanger. Highest throughputs and product feed temperatures up to 1200 °C are handled in a very compact apparatus.

Function

The Moving Bed Heat Exchanger is an indirect water-cooled or steam-heated tubular heat exchanger for fine grained, free-flowing bulk materials (see diagram, items 1,2 and 3). The heat exchanger works according to the moving bed principle, i.e. the product to be cooled forms a product bed or column (diagram, item 2) fully covering the cooling tubes (diagram, item 4), and the individual particles continuously flow downwards between these tubes. The product column rests on a discharge bottom (diagram, item 5) with variable outlet cross-section so that the amount of product discharged via the entire cooler cross-section is equal to the amount of product flowing in from the top. Operation is controlled by measuring the filling level above the cooling tubes and adjusting the opening cross-section of the discharge bottom accordingly. The cooling tubes are horizontally positioned in several rows that form a staggered arrangement so that the main product flow direction is crosswise to the tube axis and the product is turned intensely. The tubes have a patented square cross-section positioned diagonally to the vertical line. Products with an angle of repose below 45° thus also contact the bottom side of the cooling tubes (as opposed to round tubes). All these effects taken together provide for a very high heat transfer, which allows the heat exchanger to be built in very compact sizes. The cooling water or steam flow through the tubes (diagram, item 6) is in cross countercurrent to the movement of the product to be cooled.

Design features

The Moving Bed Heat Exchanger consists of several heat exchanger modules (diagram, item 7) arranged one above the other. The product leaves the heat exchanger via the discharge bottom (diagram, item 5) and a funnel (diagram, item 8). The funnel can be equipped with a collecting screw conveyor (diagram, item 9) if necessary. This does not affect the moving bed. A roof-shaped protecting screen can be installed above the heat exchanger modules to keep out agglomerates and impurities that cannot pass safely through the tube packages. Baffle plates can be installed to prevent wear of the protective screen. At the water/steam side, the ends of the heat exchanger packages (ends of the cooling water tubes) are fitted with reversing chambers (diagram, item 6) and sealed with removable end plates (diagram, item 10). On the product side, the outer tubes of the heat exchanger packages are equipped with steel plate strips at the sides (diagram, item 11). Their patented design keeps the product inside the heat exchanger - without the side walls obstructing access to the inside or interfering with the product movement. In addition, doors can be fitted (to protect the environment and the product quality).

Advantages

The Moving Bed Heat Exchanger can handle product temperatures of up to 1,200°C . Product treatment is particularly gentle. There is hardly any abrasion on the product and no measurable wear on the apparatus itself. The patented design of the faces provides for a particularly high heat transfer and full utilisation of the entire heat exchange surface. Compared with other contact coolers, this makes the Moving Bed Cooler a very compact apparatus. Access to the apparatus is excellent - the housing design provides for fast and easy cleaning both at the product and the water / steam side. The special, patented design of the sides allows the heat exchanger to be operated also without any doors, i.e. with the apparatus being open. Due to its modular design, the Moving Bed Heat Exchanger can be extended by adding further packages if necessary. Compared with fluidised bed coolers and rotary tubular coolers, the Moving Bed Heat Exchanger has a substantially lower electrical energy requirement.

Typical Applications

The Moving Bed Heat Exchanger is used for treating free-flowing bulk materials that are generally free from agglomerates, in medium and especially in high temperature applications downstream from kilns and dryers, where high amounts of heat are to be removed, large product mass flows are to be handled or compact-size units are required. Typical applications include the cooling of mineral (quartz sand, ilmenite etc.) and chemical products (NPK fertiliser, soda, FCC-catalyst, sodium tripoly phosphate "STPP“ etc.). The range of application is being constantly extended, as this relatively new technology offers potential advantages for both new and existing production processes.

Limits of Application

The Moving Bed Heat Exchanger can basically be used for free-flowing bulk goods with an angle of repose below 45° (against the horizontal axis) and particle sizes under 6 mm. The maximum product feed temperature is 1,200°C. Economic throughput rates range from 0.5 to 250 m³/h. If products are to be treated that still contain some moisture, it may be necessary to install a purge air system.