GB2287527A

GB2287527A - Drying malt

Info

Publication number: GB2287527A
Application number: GB9407766A
Authority: GB
Inventors: Thomas Nallen; John O'shea
Original assignee: MIDLAND MALTING RES Ltd
Current assignee: MIDLAND MALTING RES Ltd
Priority date: 1994-03-15
Filing date: 1994-04-19
Publication date: 1995-09-20
Also published as: BE1006522A6; IE940232A1; GB9407766D0

Abstract

A humidity detector 10 is used to continuously detect on line the humidity of air which has passed through a bed of germinated barley 2 in a kiln 1. A transducer 11 provides a signal to a fan speed controller 15 for modulating the flow of air drawn through the bed by a fan 6, at least during a "force drying" phase in which after moisture in the outer layers of the barley grains has been removed heated air moves moisture from the interiors of the grains to their surfaces. Preferably humidity is also monitored in an initial "free drying" phase in which heated air removes moisture from the surface layers of the grains and in a final curing stage in which air is passed through the bed 2 after drying is complete. <IMAGE>

Description

"Nalt Production" The invention relates malt production, and in particular to a method of kilning grain.

In particular, the invention relates to the method of kilning grain in an energy efficient manner. In a typical maltings, the largest area of energy usage is in kilning and, in general, practically all of the heat generated in the malting process is used in the kilns.

According to the invention there is provided a method of kilning grain comprising passing air through a bed of grain, wherein the humidity of the air which has passed through the bed of grain is detected and the flow of air through the grain bed is modulated in accordance with detected humidity.

In one embodiment of the invention, there is provided a method of kilning grain comprising the steps of: free drying of grain by passing free drying air through a bed of grain; force drying of the grain by passing force drying air through the bed of grain; curing the grain by passing curing air through the bed of grain; wherein, the method includes the steps, at least during the force drying stage of: detecting on line the humidity of the air which has passed through the bed of grain; and modulating the flow of air through the grain bed in accordance with the detected humidity.

In a preferred embodiment of the invention the method includes the steps of: detecting on line the humidity of the air which has passed through the bed of grain during the free drying stage; and modulating the flow of air through the grain bed during the free drying stage in accordance with the humidity detected on line during the free drying stage.

In a preferred arrangement the method includes the steps of: detecting on line the humidity of the air which has passed through the bed of grain during the curing stage; and modulating the flow of air through the grain bed during the curing stage in accordance with the humidity detected on line during the curing stage.

In a particularly preferred embodiment of the invention the flow of air through the kiln is controlled by fan means having fan speed control means and the flow of air through the bed of grain is modulated by modulating the fan speed control means.

Preferably the fan speed control means includes variable speed frequency inverter means and the detected humidity is used as the base signal for modulating the fan speed frequency inverter means.

In another aspect, the invention provides an apparatus for controlling the flow of air through a bed of grain during kilning, the apparatus comprising on line humidity detection means for detecting the humidity of the air which has passed through a bed of grain on line, and modulating means connected with the humidity detection means for modulating the flow of air through the grain bed in accordance with the detected humidity.

Preferably the modulating means includes speed control means for modulating the flow of air through a fan means.

Most preferably the fan speed control means comprises variable speed frequency inverter means for modulating the flow of air through the fan in accordance with the on line detected humidity of the air which has passed through the grain bed.

The invention also provides grain whenever kilned using the method and apparatus of the invention.

The invention will be more clearly understood from the following description thereof with reference to the accompanying drawings in which: Fig. 1 is a diagrammatic view of a method and apparatus used in kilning grain according to the invention; and Fig. 2 is a block diagram of an energy optimising system.

In general , a malting process involves taking barley at approximately 20% moisture content and drying it to 12% moisture content for storage. The barley is then steeped and the moisture content is raised 45% over a period of typically 54 hours. The steeped barley is then germinated typically over a period of five days to produce the required quantity and type of enzyme. The germinated barley is then kilned typically for a period of up to 40 hours to arrest the germination process and preserve the product for storage. Generaliy the kilning or drying is carried out by warm air at less than 1000C. Usually the barley is discharged from the kiln with under 4% moisture and stored.

Referring to Fig 1, there is illustrated in diagrammatic form a kiln 1 used for kilning a bed of grain 2. The kiln 1 has an inlet 4 for heated air and an outlet 5 for discharge of air which has passed through the bed 2 of grain. In this case the air is passed through the bed 2 of grain by means of a fan 6. The fan 6 is driven by a drive motor 7.

In the method and apparatus of the invention, a humidity detector, diagrammatically illustrated as 10, continuously detects the humidity of the air which has passed through the bed 2 of grain on line, and a transducer 11 provides a signal to a modulating means for modulating the flow of air through the bed 2 of grain. In this case, the modulating means comprises a fan speed control means 15 provided by a variable speed frequency inverter means connected to the drive 7 of the fan 6 to modulate the flow of air drawn through the bed 2 of grain by the fan 6.

In more detail, kilning involves the passage of heated air through a bed 2 of grain. As the heated air passes through the bed the moisture content of the air increases and the moisture content of the grain decreases. The temperature of the air also falls.

There are essentially three stages in kilning, namely free drying, force drying and curing or equilibrium.

During the free drying stage the outer layers of the green malt grain provide an evaporative surface from which moisture is rapidly lost. The latent heat of evaporation is provided by the incoming air and there is, therefore, a large drop in the air temperature across the bed of grain. Consequently, the air becomes saturated with moisture and the relative humidity of the air, as detected by the humidity detector 10, rises to 100%.

In this stage the volume of the air is the driving force as the moisture is being lost from the grain surface readily and the more air that is available to accept this moisture the greater the rate of drying. Consequently, during this stage, the speed of the fan 6 is modulated using the signal from the humidity detector to optimise the flow of air. In this stage generally maximum air flow is optimum.

During force drying the moisture in the surface layers of the grain is completely removed and the water diffuses from the inner layers of the grain to the surface of the grain. This diffusion process requires energy which is provided by heated air to move the moisture to the outer layer and evaporate the moisture from the surface of the grain. However, the water on the surface of the grain is not saturated as the number of water molecules available diminishes during the force drying procedure.

Consequently, the amount of moisture taken up by the air is, therefore, falling and the loss of heat for evaporation is also falling with an increasing temperature of the air which is passed through the bed 2 of grain.

The changeover from the free drying to the force drying phase is termed the "break-point".

The break-point or the transition between the free drying and force drying phase is determined on line if real time by detecting the humidity of the air using the humidity detector 10. When the humidity of the air drops below 100% the air still has drying capacity and the kilning has passed from the free drying to the force drying stage.

The force drying stage is temperature and not volume dependent.

The force drying stage continues up to the point where the available energy from the incoming heated air is insufficient to permit the water held in the centre of the grain to pass to the outside of the grain for this operation. When this stage is reached the grain is extracting as much moisture from the air as it is donating to it and essentially the system will have reached a dynamic equilibrium. In simple drying terms, the drying process is complete at this stage. If kilning continues by passing heated air into the grain at this stage the energy supplied by the heated air is essentially wasted.

We have found through extensive research and development that by continuously detecting the humidity of the air which has passed through the kiln on line, the energy usage in the electrical drive for the fans, and for heating the incoming air, is optimised. This has resulted in very substantial savings, not only in energy costs but also in optimising the residence time in the kiln. In particular, the break-point between the free drying and force drying stages can be readily determined and the speed of the fan modulated accordingly. In addition, the curing stage can be substantially shortened. Only the quantity of air and heat that is required to achieve a required condition is actually used.

Referring to Fig. 2 an energy optimising system is illustrated in more detail. It will be noted that condensing economisers 20 are used on the thermal fluid heaters 21 to produce hot water, typically at greater than 800C to preheat the air entering the kilns. In this case the thermal fluid heaters 21 are fired by heavy fuel oil.

Many variations on the specific embodiments of the invention described will be readily apparent according to the invention not limited to the embodiments hereinbefore described which may be varied in both construction and detail.

Claims

1. A method of kilning grain comprising passing air through a bed of grain, wherein the humidity of the air which has passed through the bed of grain is detected and the flow of air through the grain bed is modulated in accordance with detected humidity.

2. A method of kilning grain as claimed in claim 1 comprising the steps of: free drying of grain by passing free drying air through a bed of grain; force drying of the grain by passing force drying air through the bed of grain; curing the grain by passing curing air through the bed of grain; wherein, the method includes the steps, at least during the force drying stage of: detecting on line the humidity of the air which has passed through the bed of grain; and modulating the flow of air through the grain bed in accordance with the detected humidity.

3. A method as claimed in claim 2 wherein the method includes the steps of: detecting on line the humidity of the air which has passed through the bed of grain during the free drying stage; and modulating the flow of air through the grain bed during the free drying stage in accordance with the humidity detected on line during the free drying stage.

4. A method as claimed in claim 2 or 3 wherein the method includes the steps of: detecting on line the humidity of the air which has passed through the bed of grain during the curing stage; and modulating the flow of air through the grain bed during the curing stage in accordance with the humidity detected on line during the curing stage.

5. A method as claimed in any preceding claim wherein the flow of air through the kiln is controlled by fan means having fan speed control means and the flow of air through the bed of grain is modulated by modulating the fan speed control means.

6. A method as claimed in claim 5 wherein the fan speed control means includes variable speed frequency inverter means and the detected humidity is used as the base signal for modulating the fan speed frequency inverter means.

7. A method substantially as hereinbefore described with reference to the accompanying drawings and examples.

8. Grain whenever kilned by a method as claimed in any preceding claim.

9. Apparatus for controlling the flow of air through a bed of grain during kilning, the apparatus comprising on line humidity detection means for detecting the humidity of the air which has passed through a bed of grain on line, and modulating means connected with the humidity detection means for modulating the flow of air through the grain bed in accordance with the detected humidity.

10. Apparatus as claimed in claim 9 wherein the modulating means includes for speed control means for modulating the flow of air through a fan means.

11. Apparatus as claimed in claim 10 wherein the fan speed control means comprises variable speed frequency inverter means for modulating the flow of air through the fan in accordance with the on line detected humidity of the air which has passed through the grain bed.

12. Apparatus substantially as hereinbefore described with reference to the accompanying drawings.