Method For The Drying Of High-moisture Waste Products Of Living Organisms

Abstract

High moisture waste products of living organisms are dried by a first treatment in a continuous dehydration press, which may be a screw, followed by mechanical breakup and then immediate drying in a pneumatic conveying drier.

Description

The present invention concerns a method for the drying of high-moisture waste products of living organisms.

There are various known systems for the drying of such waste products. Thus, for instance, chicken dung is mixed with hygroscopic additives, developing heat. Then, after a sort of maturing, the cooled mixed produce is used as manure. This method has the drawback that it involves a rather long storage period of the product, and that, because of the additive, it is not possible to determine the chemical composition of the final product.

Another known method consists in drying waste products of living organisms in non-continuous drying tanks with hot air. The intermittent procedure involves much labor, and heat consumption is high.

To ensure continuous operation, a known system uses a drum drier. Heat consumption is high, and unduly long contact with the hot drier surfaces often results in the overheating or even burning of a considerable quantity of the product, with adverse effects on the quality of the final product. With the object of reducing the heat consumption of such drum driers in the treatment of fattening farm effluent, yet another known method consists in first causing the liquid to evaporate, but this requires a rather large tank with considerable ancillary apparatus. Also, the large quantity of air involved gives rise to problems of odor, which again require a large air cleansing and washing system.

On the other hand, it has long been known to drying engineers that the pneumatic conveying drier, i.e., a drier in which the stock is pneumatically conveyed by the drying air or drying gas, presents many advantages. Yet it has so far never been considered for the drying of high-moisture waste products of living organisms, as it has hitherto mainly been used for powdery products, i.e., products of quite other structures than those considered here. Also the products treated so far are mostly high-grade products warranting a certain cost for their drying, or then they are products of relatively low moisture not requiring so great a heat consumption. However, the waste products of living organisms rather involve a problem of sewage treatment (water pollution), as the products obtained, although useful, will not sell at a price sufficient to warrant a costly drying process.

By surprisingly simple means, owing to the use of a pneumatic conveying drier, the present invention permits dried products of good quality to be obtained at relatively low heat and system costs.

The method claimed hereunder is characterized in that the waste products are treated in a continuous dehydration press and immediately thereafter dried in a pneumatic conveying drier.

The sole FIGURE is a flow diagram showing an embodiment of the process of the present invention.

The first treatment of the products is in the continuous dehydration press which squeezes out much water, which then need not be evaporated. This reduces the heat requirement and the quantity of the drying air to be cleaned. Owing to the continuous process and the rapid drying in the pneumatic conveying drier, the system required for the application of the method needs little space and does not cause any problems due to intermediate storage of the products between dehydration press and drier. Drying is very rapid because the air movement is vigorous and the particles are completely enveloped by the drying air. As a result, the surface of the particles consolidates very rapidly, thus reducing the risk of a large number of overheated or burnt particles getting stuck to the drier wall and burning up.

The method is also suitable for exceptionally difficult products, provided that these, immediately after treatment in the continuous dehydration press, are mechanically broken up and fed into the pneumatic conveying drier. By the breaking-up, which can be effected by relatively simple mechanical means, the products, which are often extruded from the dehydration press in the form of a paste, are commutated and reduced to a form suitable for pneumatic conveying drying.

If the products are treated in a drier which conveys and widens out upwards, drying will be especially uniform. The velocity of the drying air is lower, and the particles cannot be entrained from the container of the drier before their weight has been reduced through sufficient drying.

Especially sticky products settling on the wall of the drier can be swept off. This is a great advantage of the pneumatic conveying drier, as it prevents any overheating of the products and thus permits the quality to be improved as compared with known methods, so that the product will in many cases fetch a higher price and thus improve the economic side of the method.

The economic side will be improved yet further if the drying and conveying air circulates in a closed circuit, so that, after separation of the dried product, part of the air passes into the cleaning system, while the other part, with fresh air added, is re-heated.

An example of the application of the method concerns solids mechanically separated (as by strainers) from stale. The stale is pumped from the stale pit, and the solids are separated by a strainer or a centrifuge. The solids, having an initial moisture of 80 to 90 percent of the wet weight, are processed by the dehydration press, having the form of a screw, to a moisture content of 40 to 50 percent of the wet weight and are then treated in the pneumatic conveying drier with drying air of 200.degree.C until their moisture content is about 15 percent. The resultant product can be used as manure. Before pressing, it is possible to add to those solids further solids obtained from a sewage treatment system arranged after the mechanical separation system. The drying air should have a temperature of at least 150.degree.C. The moisture content can range from 8 to 20 percent, depending on the composition of the final product.

In another example, stockyard waste, which may also include non-utilizable carcasses, is ground in a cylinder breaker and boiled for 20 to 30 minutes at a temperature of about 150.degree.C. If necessary, the product can further be fine-ground, and liquid fatty components separated in centrifuges. The remaining product, having a moisture of 50 to 60 percent and a temperature of about 80.degree.C, passes into the dehydration press, which squeezes out further parts of fat. Then the product, having a moisture of about 40 percent, passes into the pneumatic conveying drier, which treats it with air of 300.degree. to 400.degree.C. The product delivered by the drier has a moisture content of about 8 percent and constitutes a very valuable feed. In this case again, the pneumatic conveying drier was never before considered for the purpose, yet the squeezing-out of fat and water in the dehydration press greatly facilitates the work of the drier. Thus, the product is not exposed unduly long to high temperatures, so that the proteins and amino acids are not unduly damaged. Greaves can be similarly treated by dehydration press and pneumatic conveying drier.

Claims

We claim:

1. A method for the drying of high-moisture waste products of living organisms having a moisture content on the order of about 80- 90 percent, comprising

continuously pressing said waste products to a moisture content of about 40- 50 percent,

continuously mechanically breaking into particles said waste product from said pressing operation,

continuously passing said particles into a pneumatic conveying drier and therein simultaneously drying said particles to a moisture content between 8 and 20 percent and conveying said particles upwardly and finally out of said drier on a stream of drying air heated to at least 150.degree.C.

2. A method in accordance with claim 1 comprising effecting said drying of said particles to a moisture content of about 15 percent.

3. A method according to claim 1 wherein said waste products comprise stockyard waste.

4. Method according according to claim 1, characterized in that the products are treated in a drier which conveys and widens out in upward direction.

5. Method according to claim 1, characterized in that any products deposited on the drier wall are swept off and returned to the air stream.

6. A method according to claim 1 wherein said waste products are separated from stale.

7. A method according to claim 6, wherein said waste products further comprise solids obtained from a sewage treatment system.