Process for thermally utilizing spent grains

Details Process for thermally utilizing spent grains Process for thermally utilizing spent grains

1999-05-19

2001-01-02

Gravini, Stephen (Department: 3749)

Drying and gas or vapor contact with solids

Material treated by electromagnetic energy

Electric current applied directly through material

C034S370000, C034S378000, C034S381000, C034S397000, C034S522000, C426S231000

Utility Patent

active

06167636

ABSTRACT:

The invention relates to a process for thermally utilizing wet spent grains, wherein the wet spent grains are mechanically predried in a first drying stage, thermally dried in a further drying stage and finally thermally utilized by burning or gasification, as well as a plant for carrying out the process.
When producing beer, the wet spent grains, or brewing draff, which occur in large quantities, constitute a problem of disposal and utilization. About 20 kg of wet spent grains occur per hectoliter beer such that large-scale breweries have to dispose of, or utilize, hundreds of tons of spent grains per week.
Due to their composition, spent grains constitute a valuable fodder; it is, however, difficult to use the spent grains as a fodder in a cost-effective manner. The proper time for selling same as a fodder without problems is in winter—on the other hand, spent grains occur in larger quantities in summer than in winter. Moreover, spent grains cannot be stored without predrying. Drying is expensive, since only indirect drying is possible due to the demands set on fodder; which means poor heat transmission. Appropriate driers are expensive, involving high energy expenditures. In addition, the sale of spent grains as a fodder is going to become more and more difficult in the future because of the declining live-stock. The preservation of spent grains by fermentation again involves the disadvantage of high costs (Brauwelt No. 39 (1991), pp. 1704 to 1707).
The formation of a high-quality product for soil improvement speaks for the compostation of spent grains, yet the market is only small and production involves such high costs that it will not cover the costs, anyway.
Spent grains are also suitable for producing biogas, yet a biogas plant requires high investment costs.
An energetically practicable process for utilizing spent grains is direct burning. From the review “Brauwelt” No. 26 (1988), pp. 1156 to 1158, “Die energetische Verwertung von Biertrebern”, a process for the recovery of energy from spent grains as described in the beginning is known. Spent grain combustion plants are, however, operating at a low effectiveness because of the necessarily intensive predrying (spent grains initially containing 75 to 80% by mass of water) and the relatively poor calorific value of spent grains.
The prerequisite for an energetically optimum utilization is the attainment of auto-combustibility, which will be obtained at a H
2
O content of about 55%.
The invention aims at avoiding these drawbacks and difficulties and has as its object to provide a process of the initially defined kind as well as a plant for carrying out said process, which enable the energetically optimum, i.e., possibly profit-making utilization of spent grains. Drying of the spent grains, in particular, is to be feasible by a possibly external energy expenditure to such an extent that the spent grains can be thermally utilized, i.e., burned or gasified without back-up heating.
In a process of the initially defined kind, this object is achieved in that the mechanically dehydrated spent grains, in the further drying stage, are heated by the aid of a smoke gas occurring in the energy system of a brewery. The smoke gas occurring in the production of beer is formed by the combustion of natural gas for the purpose of generating vapor.
Besides combustion, the gasification of predried spent grains is also feasible with a combustible gas occuring as an intermediate product.
Advantageously, the gas forming during gasification is energetically utilized, preferably as an energy carrier, for the generation of vapor within the brewery system, e.g., as an additional gas to natural gas, so as to enable its energetic utilization by the brewery boiler plant through burning.
Preferably, supplementary drying aimed at eliminating capillary water by the aid of electric fields or by the aid of high-frequency fields is carried out for mechanically predrying the spent grains.
Mechanical predrying suitably is effected at least to a water content of 65 and, preferably, 62% by mass.
Suitably, solar energy may be additionally applied for the thermal drying of the mechanically predried spent grains.
The thermal drying of the spent grains advantageously is effected to a water content enabling autocombustion of the same, preferably at least to a water content of 55% by mass.
According to a preferred embodiment, pulp press water formed in mechanical predrying is treated anaerobically and the methane-containing gas formed is energetically utilized, preferably as an energy carrier for the generation of vapor within the brewery system.
Offgases forming in the combustion of the dried spent grains are disposed off along with offgases formed in a steam boiler of the brewery in a cost-effective manner.
According to a preferred variant, mixtures of spent grains and other organic biogenic waste substances are thermally utilized.
A plant for carrying out the process, comprising a mechanical drier constituting a first drying stage for spent grains and a thermal drier constituting a further drying stage for mechanically dehydrated spent grains as well as a device for thermal utilization by burning or gasifying the dried spent grains is characterized in that a duct carrying smoke gas off a steam boiler of the energy system of the brewery feeds into the thermal drier.
Preferably, the device for the thermal utilization of the spent grains comprises a combustion boiler, said combustion boiler suitably being equipped with a vapor generating means and said vapor generating means advantageously being coupled with the energy system of the brewery.
In an investment-saving manner, a smoke gas discharge duct issuing from the combustion boiler feeds into an offgas installation of a beer production plant, wherein, suitably, also an offgas duct from the thermal drier feeds into the offgas installation of the beer production plant.
According to a further preferred embodiment, the device for thermal utilization comprises a gasification means, wherein, suitably, a duct issuing from the gasification means and carrying off gases produced in the gasifier leads to a burner of a steam boiler of the energy system of the brewery.
The mechanical drier may preferably be configured as a travelling screen press or as a worm extruder.
A convection drier may suitably be employed as the thermal drier.
Preferably, the thermal drier comprises a drying means operable by solar energy.
According to a further advantageous embodiment, thermal drying, gasification and burning may be united in an apparative device, wherein, suitably, a duct carrying off the hot offgases from the device comprising thermal drying, gasification and burning is conducted directly to the steam boiler of the energy consumer of the brewery.
Thermal drying may be additionally extended by a drying means operable by solar energy.
In the following, the invention will be explained in more detail by way of two exemplary embodiments illustrated in the drawing, wherein
FIGS. 1 and 2
each depict a process scheme according to a configuration variant.
At first, the wet spent grains
1
are adjusted to a water content ranging from about 65 to 62% by mass in a first drying stage
2
in a mechanical drier
3
, which, according to
FIG. 1
, is designed as a worm press. Burning of the spent grains at such a water content is, however, not yet possible without back-up heating. For that reason, further drying is accomplished in a further drying stage
4
, in which drying of the mechanically dehydrated spent grains
5
is carried out thermally.
To this end, a thermal drier
6
designed as a tumbling drier is provided, according to FIG.
1
. The tumbling drier
6
is heated directly by smoke gas fed through duct
7
and coming from a boiler
10
installed in a beer production plant
8
. The boiler
10
is heated by natural gas, which is supplied through duct
9
; the vapor-conducting tubes are denoted by
11
. A portion of the smoke gas may be supplied directly to an offgas blower
13
of the smoke gas disposal plant via a branch duct
12
. The

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