DE2800184A1 - Drying green malt - on perforated conveyor in counterflow meandering contact path - Google Patents

Abstract

A kiln drying process for green malt uses a perforated conveyor which moves continuously and to which a hot gas flow is applied. The hot gas contacts the malt in a counterflow principle in several stages, in which the gas flows alternately upwards and downwards through the material and the belt. Arrangement combines a min. of heat input requirements with very little floor space requirements.

Description

Process for drying green malt

The invention relates to a method for kilning green malt, which is located on a gas-permeable floor and exposed to heated gas will.

The drying and kilning of green malt is traditionally carried out in Kilns, which have a stationary sieve bottom, through the gas heated from below is directed until the green malt has passed the various drying and / or kilning stages has gone through. The heated gases are either heated air or around combustion gases mixed with drying air. This is called indirect or immediate heating.

During the production of malt, the product goes through a drying phase, which has the task of chemically biological reactions by dehydration To bring it to a close and give the malt a certain character depending on its intended use and to give it a corresponding color.

On average, 750 kg of water is removed from one ton of finished malt, i.e. the bulk weight is 1750 kg.

Even though there is only a theoretical heat requirement to evaporate this amount of water of 435,000 kcal is required, are required by those in use today Single-tray high-performance kiln with direct, lossless firing an amount of heat from 800,000 to 1,050,000 kcal. This poor utilization rate is due to the following circumstances due to: The evaporation of the water in the green malt takes place by preheated Air, which after flowing through the drying material, the kiln with a temperature leaves, which on an annual average is significantly above the outdoor air condition.

The intermittent 24-hour operation of the kiln (6 - 9 p.m. kiln, 3 - 6 h loading and unloading) requires the equipment and building structure to cool down, which have to be reheated together with the malt at the beginning of the kiln.

As a result of the large temperature differences between kiln air and Outside air is lost through the building structure in the form of transmitted heat.

For technological reasons, the air inlet temperature into the Green malt and thus also the water absorption capacity the air is limited. Most of the water is also removed within the first 8 to 12 hours, so that the ventilation systems are dimensioned for this period of time. In the legal 6 to 12 hours, the system works with reduced power and accordingly poor use of the drying effect.

In addition, the short full-load operating time and the supply air temperature limitation large amounts of air are circulated, which are accordingly at the cost of the ventilation components such as blower, drive, air heater, Air ducts etc. have a negative effect.

An overview of the methods used so far is in the book "The brewery, technology of malt preparation", pages 277 to 283 and 291 to 297 included.

The invention avoids these disadvantages. It is based on the task to propose a method for drying and kilning of green malt, which works through characterized by a low energy requirement and space requirement.

To solve this problem, the invention is characterized in that that the heated gas in several stages in a countercurrent process in contact with the Material to be dried is brought.

The material to be dried, for example malt, is relatively thin Layer about 10 to 30 cm on a slow moving or at short intervals conveyor belt moving forward step by step through the drying system. The process air or drying air is countercurrent to the conveying direction of the material to be dried conveyed through the estate in at least four stages. With an appropriate arrangement of preheaters, bypass valves, blowers and reheaters can be found in the malt kiln normal operating conditions can be achieved with significantly lower energy consumption.

Preferred embodiments of the subject matter of the invention result from the subclaims.

The invention will be described in the following on the basis of an exemplary embodiment explained in more detail, from which more detailed explanations regarding the mode of operation and of the advantages of the invention.

The figure shows schematically a partially sectioned side view a multi-stage continuous kiln according to the invention.

An air-permeable conveyor belt 7 conveys items 8 to be dried slowly from a loading station 13 to a clearing station 14 by steps 6 to 1, where drying air flowing in the opposite direction gives the good 8 the required Amount of water is withdrawn.

Between the first in the flow direction of the drying air Stage 1 and stage 2 a preheater 9 is attached, which the process air heated to the technologically correct drying temperature. This preheater can also be designed in several parts, with waste heat in the first part, e.g. condenser heat by the chillers, and the second part as a conventional burner generates the residual heat.

Via a bypass flap 10, the subsequent stage 3 can receive cold air are fed directly from stage 1 via a flow channel 16 in which a bypass valve 10 is located, via which the amount of air flowing through the channel 16 is set. This cold air becomes the heated air flowing through stage 2 Air mixed in, so that the technologically correct simmering temperature in the stage 3 is reached.

At this point it should be mentioned that stage 1 is either air at ambient temperature or preheated air is supplied via a heat exchanger.

A fan 11 then promotes the mixture produced in stage 3 through the following stages 4 and 5, where as a result of the intensive water absorption eireCooling of the process air entry. Between level 5 and the subsequent stage 6, a reheater 12 is arranged, which of the consumed Process air again lends a water absorption capacity, and also as a waste heat exchanger can be operated.

Another type of reheating operation is the process air flow after stage 3 to extract heat via an air cooler and this to the reheater, for example via a water cycle.

The multi-stage through-feed kiln described is also suitable for Use of an exhaust air heat recovery system, where 15 energy is transferred from the warm to the cold air flow. The heat exchanger is a recuperative one Air-to-air heat exchanger.

The multi-stage through-feed kiln points to those known today Kiln systems have the following improvements: 1) By extending the drying time to 24 hours a day and by increasing the water absorption capacity of the process air as a result of the high initial temperature and reheating, the size of the ventilation system is reduced Devices by approx. 75%; the devices and thus the enclosed space are significantly smaller, which has a positive effect on both costs and energy requirements.

2) As the heating and drying phase as a preliminary stage for the withering is used, the heat requirement is reduced by approx. 30%.

3) Serves by arranging the preheater after the first stage this as a cooling zone, with the removed from the drying goods and conveyor belt Heat is fully transferred to the process air.

4) Continuous operation allows more economical waste heat recovery of systems with similar operating conditions, e.g. cooling systems in the germination boxes. The same also applies to the recuperative air-to-air heat exchanger system.

5) the low air throughput and the correspondingly low pressure loss the thin layer of malt results in very low connection values for the fan drive, whereby the power consumption also takes into account the 24-hour full load operation still makes up approx. 25% of today's values.

The execution described in the example is only one possible Production method of the multi-stage through-feed kiln.

Instead of the circulating conveyor belt, a circular, Air-permeable sieve can be used, with the air passing through carved segments flows and the material to be dried is transported by slowly turning the sieve.

The transport route, be it a longitudinally moving belt or the rotating one Sieve, can also be split on two or more levels. Also is the promotion of the items to be dried not only horizontally, but also at an angle or vertically Direction possible.

Instead of green malt, other items to be dried can also be used with the one described Method and the device described are dried in an energy-saving manner. Described became a through-feed kiln with six stages. Six stages are not necessary; man can also get by with more or fewer steps. It is preferred if at least four stages are provided. As the arrows drawn in the figure show, the drying air flows through the conveyor belt with the items to be dried Exit of each stage, for which purpose corresponding chambers with walls 17 are formed which force this zigzag flow path on the drying air. Through this the item to be dried is removed from the top and then from the bottom Drying air flows through. Instead of drying air, an air mixture can also be used be used with exhaust gases.

Claims (7)

P a t e n t a n s r ü c h e 1. Process for kilning green malt, which is located on a gas-permeable floor and exposed to heated gas it will be shown that the heated gas in several Steps (1 - 6) brought into contact with the material to be dried (8) in a countercurrent process will. 2. The method according to claim 1, d a d u r c h g e k e n n -z e i c h n e t that a preheater downstream of a first stage (1) in the direction of flow of the gas (9) is provided through which at least some of the gases flow. 3. The method of claim 1 or claim 2, d a d u r c h g e k It is noted that the flow rate between two stages is via a bypass channel (16) is adjustable. 4. The method according to claims 1 to 3, d a d u r c h g e k e n n e i c h n e t that in one of the stages the flow is caused by a fan (11) is supported. 5. The method according to claims 1 to 4, d a d u r c h g e k e n It is not clear that in one of the last stages the gas is passed through a reheater (12) is heated. 6. The method according to claims 1 to 5, d a d u r c h g e k e n It is noted that the gas flowing into the first stage (1) is in a heat exchanger (15) by which the last stage (6) flowing gas is preheated. 7. The method according to claims 1 to 6, d a d u r c h g e k e n n z e i c h n e t that the material to be dried (8) is on a gas-permeable conveyor belt (7) is funded by the stations.