GB2457091A

GB2457091A - Batch process and apparatus for kilning germinated grain

Info

Publication number: GB2457091A
Application number: GB0801985A
Authority: GB
Inventors: Peter Nallen
Original assignee: MINCH NORTON Ltd
Current assignee: MINCH NORTON Ltd
Priority date: 2008-02-04
Filing date: 2008-02-04
Publication date: 2009-08-05
Anticipated expiration: 2028-02-04
Also published as: GB2457091B; GB0801985D0

Abstract

A batch process and apparatus for kilning germinated grain having a moisture content of between 40% and 50% by weight is disclosed. The kiln apparatus 1 comprises a lower kilning bed 4 for curing germinated grain, an upper kilning bed 3 for withering germinated grain, an ambient air inlet 7, a flue outlet 8, an air heater 9 and a pair of impeller fans 13a, 13b. The lower kilning bed has an inlet for kilning air and an outlet for delivery of air, which has passed through the lower kilning bed, to the inlet of the upper kilning bed. The upper kilning bed has an inlet for kilning air and an outlet for delivery of air, which has passed through the upper kilning bed, to the inlet of the flue. The air heater is designed to directly heat the air to a temperature of 50-70{C, preferably 55-65{C. The air heater may comprise a pre-heater 9a, a main heater 9b, a burner 10 and an exhaust flue 11. The impeller fans provide an airflow rate of 630,000-700,000 cubic metres per hour across the lower kilning bed and a rate of 630,000-760,000 cubic metres per hour across the upper kilning bed. Preferably, the kiln apparatus comprises a flue air heat exchanger 12 for recovering heat from the heated air which has passed through the kilning beds.

Description

"A batch process and apparatus for kilning germinated grain"

Introduction

The present invention relates to a batch process for kilning germinated grain having a moisture content of between 40% and 50% by weight. The invention also relates to an apparatus for batch kilning of germinated grain having a moisture content of between 40% and 50% by weight.

Kilning is the final process in the malting of grain. It is essentially a drying process where hot air is used to dry grain following steeping and germination to provide malted grain or malt having a moisture content of generally between 2% and 5% by weight.

In the specification the term "by weight" refers to the weight of the grain except where otherwise specified.

There are essentially two main types of kilning processes namely batch and continuous kilning processes. The main drawback with previous batch kilning processes is that they have been found to be inefficient. Specifically, heretofore batch kilning has been a time consuming process, generally taking in excess of 21 hours and usually more than 23 hours on the basis of a batch of between 235 and 245 tonnes of grain and further details of the disadvantages of batch kilning are outlined in US Patent No. 6,070,520. The invention disclosed in this US Patent document overcomes the disadvantages of batch kilning by developing a continuous or substantially continuous process and apparatus for drying of malt.

Thus although it is recognised that continuous kilning solves some of the problems associated with batch kilning inefficiency, the continuous processing of malt itself has been found to lead to problems with malt quality. Specifically, due to the nature of continuous kilning, it is more difficult to control the level of drying of the grain thus resulting in malt with inhomogeneous moisture contents. Additionally, continuous kilning provides limited access to the grain thus preventing segregation of the grain on the basis of protein content and other parameters, therefore increasing the level of inhomogeneity in the resultant malt.

Thus there is a need for a more efficient batch process and apparatus for kilning germinated grain.

Statements of Invention

According to the invention, there is provided a batch process for kilning germinated grain having a moisture content of between 40% and 50% by weight, the process comprising: delivering between 235 and 245 tonnes of germinated grain to an upper kilning bed and reducing the moisture content of the germinated grain in the upper kilning bed to between 10% and 14% by weight in a withering time of between 4 and 8.5 hours; delivering between 235 and 245 tonnes of partially kilned germinated grain to a lower kilning bed and reducing the moisture content of the partially kilned germinated grain in the lower kilning bed to between 2% and 5% by weight in a curing time of between 10 and 14.5 hours; the kilning process comprising the steps of: delivering air to an air to air heater; the air to air heater directly heating the air to a temperature in the region of between 50°C and 70°C; supplying the directly heated air to the lower kilning bed; drawing air from the lower kilning bed to provide an airflow rate of between 630,000 and 700,000 m3/h across the lower kilning bed; and supplying air to the upper kilning bed to provide an airflow rate of between 630,000 and 760,000 m3/h across the upper kilning bed.

It has surprisingly been found that by directly heating the air to a desired temperature the resultant hot air has a more uniform temperature. Additionally, as the air is directly heated, there is less restriction in the air flow during heating, thus the air is subsequently heated up quicker and less air is lost to the atmosphere.

Due to the increased rate of heating of the air, the air flow rate can also be increased through the kilning beds as the air is at a more uniform temperature as a result of direct heating. This leads to a reduction in the overall kilning time. The rate of drying of the grain and the total time required to reach the desired grain moisture level is also significantly reduced. Thus as a result of the increased kilning rate, larger batches of grain can be dried at any one time. Due to the improved kilning process of the invention, it has been found that the capacity of grain which can be kilned annually has increased by 25%. Thus on the basis of a 365 day malt production plant with batches of between 235 and 245 tonnes, the malt capacity has increased by an additional 2000 to 2500 tonnes.

It has also surprisingly been found that by directly heating the air and increasing the air flow rate through the kilning beds that the resultant grain moisture level is more uniform. Accordingly a larger quantity of the resultant malt is within the required malt moisture specification. This has led to improved repeatability in malt moisture levels and a reduction in grain spoilage.

Additionally, due to direct heating, heat transfer losses are decreased and a more efficient use of the nitrogen oxide gas used to heat the air is achieved, It has been surprisingly been found that the amount of nitrogen oxide gas consumed per tonne of finished malt is 12.5% less than in previous kilning systems. The overall result is a more efficient and a more effective kilning process.

Preferably, air is drawn from the lower kilning bed to provide a pressure drop of between 270 and 300Pa across the lower kilning bed.

Further preferably, air is supplied to the upper kilning bed to provide a pressure drop of between 190 and 300Pa across the upper kilning bed.

The advantage of reducing the pressure drop is that there is less resistance across the grain and hence the hot air will pass through the kilning beds at a more efficient rate thus allowing faster kilning, and in combination with the more controlled air temperatures due to direct heating, more homogenous kilning.

Preferably, the air temperature, air flow rate and pressure are controlled to as to ensure that the kilning process takes not more than 23 hours.

Further preferably, air temperature, air flow rate and pressure are controlled to as to ensure that the kilning process takes between 14 and 21 hours.

Ideally, the withering time is between 7 and 8 hours.

Preferably, the curing time is between 12.5 and 13 hours.

Further preferably, the air is directly heated by the air to air heater to a temperature in the region of between 55°C and 65°C.

According to the invention, there is also provided an apparatus for batch kilning germinated grain having a moisture content of between 40% and 50% by weight, the apparatus comprising a vertical kiln having: an upper kilning bed for withering of the germinated grain, a lower kilning bed for curing of the germinated grain, an inlet for ambient air and a flue outlet; the upper kilning bed having an inlet for kilning air and an outlet to the flue; the lower kilning bed having an inlet for kilning air and an outlet for delivery of air which has passed through the lower kilning bed to the inlet of the upper kilning bed; the apparatus further comprising: an air to air heater for directly heating air to a temperature in the region of between 50°C and 70°C; and a pair of impeller fans for drawing air from the lower kilning bed to provide an airflow rate of between 630,000 and 700,000 m3/h across the lower kilning bed and for supplying air to the upper kilning bed to provide an airflow rate of between 630,000 and 760,000 m3Ih across the upper kilning bed.

Preferably, the impeller fans draw air from the lower kilning bed to provide a pressure drop of between 270 and 300Pa across the lower kilning bed and supply air to the upper kilning bed to provide a pressure drop of between 190 and 300Pa across the upper kilning bed.

According to the invention there is further provided malt whenever produced by the process of the invention and/or using the apparatus of the invention.

Detailed Description of the Invention

The invention will be more clearly understood from the following description thereof given by way of example only with reference to the accompanying drawing in which; Fig. 1 is a cross-sectional view of the kiln according to the invention; Referring to Fig. 1, there is provided a kiln, indicated generally by reference numeral 1, having an exterior wall 2, an upper kilning bed 3 and a lower kilning bed 4. Each of the upper and lower kilning beds 3, 4 have a perforated floor indicated by the reference numerals 5, 6 respectively. The kiln further comprises an air inlet 7 for ambient air and a flue outlet 8 through which exhaust air used in the kilning process is discharged.

An air to air heater 9 is further provided for directly heating the air. The air to air heater 9 comprises a pre-heater 9a and a main heater 9b, the pre-heater 9a being located upstream of the main heater 9b. The air to air heater 9 also comprises a burner 10 and exhaust flue 11. The kiln 1 further comprises a flue air heat exchanger 12 for recovering heat from heated air which has passed through the kilning beds 3, 4.

The heat recovered is directed to the pre-heater 9a for direct heating of incoming ambient air. In turn, any heat lost between the pre-heater 9a and the main heater 9b is directed to the heat exchanger 12 and this recovered heat is also subsequently directed to the pre-heater 9a for direct heating of incoming ambient air.

The kiln 1 further comprises a pair of impeller fans 13a, 13b in parallel for drawing air up or sucking air through the lower kilning bed 4 and supplying or blowing air up through the upper kilning bed 3.

In use, germinated grain which has been steeped and treated in germinating vessels is first delivered to the upper kilning bed 3. When the moisture level of the grain in the upper kilning bed 3 has been reduced to a desired level the grain is then delivered to the lower kilning bed 4 for further reduction of the grain moisture level. Ambient air enters the kiln 1 through the air inlet 7 and is delivered to the pre-heater 9a where the ambient air is directly heated so as to raise the temperature by 10°C to 20°C. The pre-heated air is then delivered to the main heater 9b where the air is further directly heated so that the temperature of the air is raised to between 50°C and 70°C. Hot kilning air is delivered from the main heater 9b through the perforated floor 6 of the lower kilning bed 4. This air is drawn through the lower kilning bed 4 by the impeller fans 1 3a, 1 3b and is then blown by the impeller fans 1 3a, 1 3b through the perforated floor 5 of the upper kilning bed 3. The air blown through the upper kilning bed 3 is then directed to the flue air heat exchanger 12 where the heat is recovered and passed to the pre- heater 9a. The air exits the kiln through the flue outlet 8.

Fig 1 discloses a pair of air to air heaters 9a, 9b with associated burners 10 and exhaust flues 11 and a pair of heater exchangers 12 with respective inlets 7 and outlets 8, it is envisaged however that the apparatus could operate efficiently with one of each. The air to air heater directly heats the ambient air. The air to air heater described is a gas fired heater, however it is envisaged that any suitable air to air heater could be used. The gas in the chamber of the air to air heater is usually nitrogen oxide and is generally produced by means of a burner and an internal flue gas recirculation system. The flue gas then flows through a single stage tube bundle, transferring heat energy into the ambient kiln air flowing over the outside of the tube bundle. Flue gas on the inside of the tube bundle is always on a negative pressure therefore there is no risk of nitrogen oxide flue gas entering the kiln air. Heat from the hot flue gas leaving the tube bundle can be recovered with another fan system and can be used as primary heat for the gas burner air.

The orientation and positioning of the heaters are designed to optimise operational performance as well as allow ease of maintenance and cleaning. The installation position of the heaters is between 450 and horizontal with respect to the other components of the apparatus.

As previously mentioned, the kiln comprises a pair of impeller fans in parallel, one of which is positioned on the left side and the other on the right side of the kiln. The airflow rate through the kilning beds is controlled by both the size impeller fans and the speed of the variable speed drives on the motors driving the fans. The airflow rate can be further increased by reducing the pressure across each of the kilning beds. As the air temperatures achieved by the air to air heater are more controlled, higher air flow rates can be used while still ensuring that uniform kilning of the grain is being carried out. Higher air flow rates lead to faster kilning of the grain and in combination with the direct heating of the air lead to more homogeneous kilning of the grain. Thus it is not a further increase in air temperatures which one would expect which has an effect on the rate of kilning but rather the manner in which the air is heated, which allows higher flow rates to be used, and in combination with their flow rates increases the overall kilning rate and results in more uniform kilning of the grain. A standard batch kiln generally processes between 235 and 245 tonnes of grain per cycle and thus kilning times and reduction in kilning times are specified on this basis.

Example 1:

484 tonnes of barley was obtained which comprised 242 tonnes of partially kilned barley having a moisture content of 12% and 242 tonnes of germinated barley having a moisture content of 44%. The partially kilned barley was transferred to the lower kilning bed and the germinated barley was transferred to the upper kilning bed. Air entered the system and was directly heated by the air to air heater to 55°C. The air was sucked up through the lower kilning bed and was blown up through the upper kilning bed by the impeller fans. The impeller fans had a diameter of 1300mm and a width of 1360mm with double sided intakes.

The total pressure loss across the upper kilning bed was measured as 300 Pa.

This corresponded to a flow rate of 320000 m3/h at an air density p = 1.2 kg/m3 using a fan graph for 900 1/mm. The change of the air density subject to temperature increase was also considered to obtain an accurate result.

The air off the upper kilning bed had a temperature of 28.8°C, and a relative humidity of 100%. The density of the air was measured as 1.14 kg/rn3 and the air flow rate was corrected by multiplying with the factor 1.14/1.2. The measured airflow therefore should have equalled about 336.842 x 2 (as there were two fans) = 673.684 m3/h.

The temperature of the air off was measured as 29.5°C, and the relative humidity was estimated as 100%. The density of the air off was measured as 1.4 kg/rn 3 using a Mollier h,x diagram.

The left side fan had an airflow of 337,613 m3/h, whereas the right side fan had an airflow of 356,638 m3/h. The total airflow was 694,251 m3/h and the total pressure loss per fan (p upper deck' 280 Pa +1-5 Pa). The efficiency was calculated as 75%.

As the airflow was even throughout the upper kilning bed, this suggested an appropriate and even kiln loading. The total air-flow was increased to 380,000 m3/h (per fan) = total 760,000 m3/h by reducing the total pressure losses down to 190 Pa (900 1/mm, r = 60%). This results in an increase of air-flow of up to 2 x 10,000 (2 x 15,000) m3/h = 2.8-4.3 %, which led to a total kilning time of between 16.5-16.2 his.

Example 2

The hot air temperature was increased to 65°C by the air to air heater while also decreasing the absolute air humidity from around 13.2 g/kg to 8.5 glkg. This resulted in an increase in drying capacity of in the region of 35%. The temperature gradient within the bed layer increased to 60°C resulting in an average further increase in drying capacity of 23% thus indicating that up to 23% or up to (potentially) 4 hrs less time was required to reach the break-point in the top layer.

This reduced the curing time by about 1-2 hrs on average depending on malt quality processed, i.e. a subsequent reduction of 1 to 2 hours less kilning time.

Table 1 shows the change in parameters of a standard kiln as compared to a new kiln and kilning process of the present invention.

Table I

Parameter Standard Batch New Batch Kiln Kiln Grain capacity per annum (tonnes) 81,000 Additional 2000-based on batches of between 235 to 2500 245 tonnes Pressure loss across lower bed (Pa) 300 -350 270 -300 Flow rate through lower bed (m3/h) 580,000-630,000 630,000 -700,000 Pressure loss across upper bed (Pa) 250 -350 190 -300 Flow rate through upper bed (m3/h) 580,000 -630,000 630,000 -760,000 Total kilning time (hours) > 21 14 -21 In the specification the terms "comprise, comprises, comprised and comprising" or any variation thereof and the terms "include, includes, included and including" or any variation thereof are considered to be totally interchangeable and they should all be afforded the widest possible interpretation and vice versa.

The invention is not limited to the embodiment hereinbefore described, but may be varied in both construction and detail within the scope of the appended claims.

Claims

CLAiMS 1. A batch process for kilning germinated grain having a moisture content of between 40% and 50% by weight, the process comprising: delivering between 235 and 245 tonnes of germinated grain to an upper kilning bed (3) and reducing the moisture content of the germinated grain in the upper kilning bed (3)to between 10% and 14% by weight in a withering time of between 4 and 8.5 hours; delivering between 235 and 245 tonnes of partially kilned germinated grain to a lower kilning bed (4) and reducing the moisture content of the partially kilned germinated grain in the lower kilning bed (4) to between 2% and 5% by weight in a curing time of between 10 and 14.5 hours; the kilning process comprising the steps of: delivering air to an air to air heater (9); the air to air heater (9) directly heating the air to a temperature in the region of between 50°C and 70°C; supplying the directly heated air to the lower kilning bed (4); drawing air from the lower kilning bed (4) to provide an airflow rate of between 630,000 and 700,000 m3/h across the lower kilning bed (4); and supplying air to the upper kilning bed (3) to provide an airflow rate of between 630,000 and 760,000 m3/h across the upper kilning bed (3).
2. A process for kilning germinated grain as claimed in claim 1, wherein air is drawn from the lower kilning bed (4) to provide a pressure drop of between 270 and 300Pa across the lower kilning bed (4).
3. A process for kilning germinated grain as claimed in claims 1 or 2, wherein air is supplied to the upper kilning bed (3) to provide a pressure drop of between 190 and 300Pa across the upper kilning bed (3).
4. A process for kilning germinated grain as claimed in any of claims 2 or 3, in which the air temperature, air flow rate and pressure are controlled to as to ensure that the kilning process takes not more than 23 hours.
5. A process for kilning germinated grain as claimed in any of claims 2 to 4, in which the air temperature, air flow rate and pressure are controlled to as to ensure that the kilning process takes between 14 and 21 hours.
6. A process for kilning germinated grain as claimed in any preceding claim, wherein the withering time is between 7 and 8 hours.
7. A process for kilning germinated grain as claimed in any preceding claim, wherein the curing time is between 12.5 and 13 hours.
8. A process for kilning germinated grain as claimed in any preceding claim, wherein the air is directly heated by the air to air heater (9) to a temperature in the region of between 55°C and 65°C.
9. A process substantially as described hereinbefore with reference to the accompanying examples and drawing.
10. An apparatus for batch kilning germinated grain having a moisture content of between 40% and 50% by weight, the apparatus comprising a vertical kiln (1) having: an upper kilning bed (3) for withering of the germinated grain, a lower kilning bed (4) for curing of the germinated grain, an inlet (7) for ambient air and a flue outlet (8); the upper kilning bed (3) having an inlet for kilning air and an outlet (8) to the flue; -12-S the lower kilning bed (4) having an inlet for kilning air and an outlet for delivery of air which has passed through the lower kilning bed (4) to the inlet of the upper kitning bed (3); the apparatus further comprising: an air to air heater (9) for directly heating air to a temperature in the region of between 50°C and 70°C; and a pair of impeller fans (13a, 13b) for drawing air from the lower kilning bed (4) to provide an airflow rate of between 630,000 and 700,000 m3/h across the lower kilning bed (4) and for supplying air to the upper kilning bed (3) to provide an airflow rate of between 630,000 and 760,000 m3/h across the upper kilning bed (3).
11. An apparatus for kilning germinated grain as claimed in claim 10, wherein the impeller fans (13a, 13b) draw air from the lower kilning bed (4)to provide a pressure drop of between 270 and 300Pa across the lower kilning bed (4) and supply air to the upper kilning bed (3) to provide a pressure drop of between and 300Pa across the upper kilning bed (3).
12. An apparatus substantially as described hereinbefore with reference to the accompanying examples and drawing.