Saving of primary energy in breweries.
Breweries require significant amounts of energy in the forms of heat and electricity for the production and bottling of beer. Mostly they generate the heat required by the combustion of coal oil and gas and obtain the electrical energy from an electricity generating station.
The heat requirements of breweries at the end of the 1950s and the beginning of the 1960s was still some 100 [kWh.sub.th] and the electricity consumption some 12 to 15 [kWh.sub.el] per hectoliter ready-for-sale beer (RSB). Today, by improved plant engineering, more sparing use of hot water and better technology in general, it has been possible to reduce these values considerably (Table 1). For example, in the Federal Republic of Germany, the energy savings associated with the production of some 90 million hectoliters per year have already reached considerable values. Development has, nonetheless, not been allowed to stand still. [Tabular Data Omitted]
A market enthusiasm for further developments in the interest of improved economic performance as regards energy exploitation, better technology and even greater respect for environmental protection aspects has been apparent precisely in recent years . This trend has resulted in:
- closed cooking under pressure or pressure-less cooking in conjunction with a thermal accumulator or vapor compression system.
- high-temperature wort cooking.
- brewing hot water production from wort cooling.
- cylindro-conical fermentation tanks featuring high coolant temperatures.
Another noteworthy development here is the significantly lower water consumption: i.e. in the 1950s, 12 to 15 hl per hectoliter RSB, compared with about six hl today. In parallel, it has also been possible to reduce the hot water consumption and thus the heat requirement to a marked extent.
Breweries which still utilize the standard procedure of taking the service water from the copper vapor condensation plant and the brewing hot water from the wort cooling, require, in the presence of the usual boiler and other plant efficiencies, 50 to 60 k Wh/hl RSB.
This amount is divided between:
- 18 to 22 [kWh.sub.th]/hl RSB in the brewhouse production block.
- 25 to 30 [kWh.sub.th]/hl RSB in the bottling and keg filling block.
- 5 to 10 [kWh.sub.th]/hl RSB in the remaining production procedures, i.e. vaporization, sterilization, cleaning, heating and general losses.
The heat requirement in the brewhouse depends on the type of mash process, as well as on the duration and intensity of the wort cooking. Different sorts of beer require in part different mash processes, evaporation rates and cooking times. As a function of the original wort content, they also require different mash and wort quantities. In the case of beers produced by sedimentary fermentation in the normal original wort range, a distinction is drawn between the infusion process and the two-mash process. The wort cooking has an overall evaporation rate of between 8 and 12 percent, referred to the hot finished wort at cooking times of between 60 and 90 minutes per brew. Table 2 shows the heat requirement of the brewhouse. [Tabular Data Omitted]
Heat Provision Requirements
It has to be possible to heat up the total mash quantity, having 0.7 hl of finished wort (FW) per hectoliter, at a temperature rise of 0.9 to 1.0 K/min. Moreover, during the heating up process, it is necessary to have as uniforma distribution of temperature as possible within the mash.
During the two-mash process, the part or cook mash having 0.21 to 0.24 hl of FW per hectoliter should be heated up in the temperature range 60 to 75 degrees Celsius at a temperature rise of 1.5 or, better, 2.0 K/min. The temperature differences in the mash don't have to be greater than 1 K and, at the end of each heating-up stage, should be equalized out within half a minute. The mash vessels used nowadays, with not too high a mash level and gentle but intensive mixing by stirring, require a steam overpressure of 200 to 250 kPa.
The run-off wort has a temperature of 74 to 75 degrees Celsius and has to be brought to the cooking temperature. Depending on the brewing sequence, 15 to 45 minutes are to be provided for this purpose. The wort quantity to be heated up, also called the "copperfull" quantity, amounts to 8 to 12 percent, depending on the programmed overall evaporation rate, i.e, 1.08 to 1.12 times the finished quantity.
Heating up is accomplished in 30-45 minutes via the heating surfaces of the wort coppers (base heating surface, internal cooker, external cooker). Shorter heating-up times can usually only be achieved via plate-type heat exchangers.
Nowadays, with normal overall evaporation rates of 8-10 percent, the wort cooking times amount to 60 to 90 minutes. The wort is not to be exposed to temperatures above those specified. According to present day knowledge, wort temperatures at the cooker outlet of 103 to maximum 104 degrees Celsius are optimum. This is known as "gentle cooking."
This gentle cooking implies, however, that steam temperatures are to be as low as possible. Since the values of 103-104 degrees Celsius at the cooker outlet are mixture temperatures, the limit temperature at the walls of the tubes or plates is higher. Hence a saturated steam temperature of 108 to maximum 110 degrees Celsius is desired. However, large heating surfaces can only be provided as external cookers. This means that a saturated steam temperature of up to 130 degrees C. has to be accepted from cost and space considerations.
It should be noted also that low heating steam temperatures lower the rate of coating of the heating surface with albumen, and thus alleviate the periodic cleaning required (e.g. once per week). Figures 1&2 show the individual brews as a function of time.
Heat Recovery Possibilities
In the case of infusion mash processes, heat recovery is not possible, since the total mass is heated up only to a maximum of 76 degrees C. and no part mashes are cooked.
On the other hand, during the one-mash or two-mash process, in each case 30-35 percent of the total mash is heated up to cooking temperatures and then cooked for 10-15 minutes. The cooking vapors thus emitted can be passed into a closed copper vapor condenser, condensed and then cooled from 85 to about 30 degrees C. The thermal energy thus released is used to obtain process hot water; about 0.06 hl per hectoliter RSB from the one-mash process or some 0.12 hl from the two-mash process. The process hot water requirement of a brewery is nowadays in the range of 0.3-0.4 hl per hectoliter RSB. Hence 30-40 percent of this quantity could be covered by suitable exploitation of waste heat from the two-mash process. However, should it be necessary during the infusion mash process to obtain this 0.12 hl process hot water by using live steam, some 1.5 [kWh.sub.th] of fuel per hectoliter RSB have to be used. Comparing the primary heating energy savings of the infusion process with those of the two-mash process (which involves obtaining 1.23 [kWh.sub.th] per hectoliter of RSB from fuel), the decision for or against the infusion process is no longer based on energy economic performance aspects, but is derived only from technical and technological considerations.
The heat in the cooking vapors can be utilized in various ways. Formerly, hot brewing water was produced in the vapor condenser linked to the copper. Today, however, hot brewing water is obtained in sufficient quantity and temperature from the closed circuit wort cooking.
Formerly, the amounts of process hot water were very large at the then unusual high overall evaporation rates of 10-15 percent. Moreover, at least 30-35 percent of the heat contained in the vapors was carried away by the air passing through the open wort cooking system.
Using closed pressure or pressure-less cooking and improved cooking technology in conjunction with a more sophisticated wort analysis, it has been possible to reduce the cooking times to 60-90 minutes and the overall evaporation rates to 8-10 percent, maximum 12 percent. The process hot water quantity obtained in this way is, however, in the presence of full exploitation of waste heat sources, still too large (0.7 to 0.9 hl per hectoliter RSB).
The following heat recovery systems have become established in connection with wort cooking:
- warming up of hot water (about 95 degrees C.) which is stored during the cooking phase and then used in a closed circuit to heat up the wort from 74/74 degrees C. to about 92 C.
- compression of the cooking vapors in a vapor compression plant; these vapors are then used to cook the wort.
During vapor compression (VCP), the vapors are extracted from the copper and compressed. The heat energy contained in same is then transferred via condensation in the external cooker to the wort which is to be cooked (Fig. 3). No further direct comment will be made in this paper concerning the effectiveness of a vapor compression plant and its possible influence on the quality of the cooking. The basic technical requirements for a vapor compression system:
- closed cooking system, no air passing through.
- external cooker (tube- and platetype cooker), operating at 30 to maximum 40 kPa overpressure.
- controlled wort outlet temperature (103 to maximum 104 degrees C.) from the cooker.
- controlled wort circulation quantity; practically all the wort is acquired from the wort copper (frequency-controlled circulation pump, wort feedback into the wort boiler so as to improve the flow characteristics).
- not affected by the hop resin and carbon dioxide components in the cooking vapors, injection cooker to lower the temperature of the compressed and thus superheated vapor mixture to the saturation temperature.
- vapor mixture condensate cooler to lower the temperature of the cooking vapor mixture condensate from 100 to about 30 degrees C. with associated production of process hot water (85 degrees C.).
The vapor compression system, which in general is designed for an evaporation rating of about 8 percent per hour referred to 1 hl of finished quantity, provides the desired technological and also energy economic performance advantages, i.e.:
- low wort outlet temperature from the cooker (is greater than or equal to) or -]104 degrees C.)
- low heating steam temperature (is greater than or equal to) or -]110 degrees C.).
- Purpose-oriented wort handling with appropriate layout of the copper.
- best possible exploitation of the cooking vapors from the energy economic performance aspect, irrespective of the duration of the cooking.
- utilization of the residual heat in the vapor condensate by cooling same down to about 30 degrees C. The amount of process hot water (at 85 degrees C.) which is thereby obtainable still amounts to about 0.011 hl per percent overall evaporation rate and hectoliter RSB.
The electricity consumption of a vapor compression plant is 0.3 to 0.4 [kWh.sub.el] per hectoliter FW, depending on the rate of evaporation and on the duration of the cooking.
Rational Energy Utilization
Rational energy utilization can be obtained by using a cogeneration type packaged heat-and-power station . A packaged heat-and-power station module is made up of an internal combustion engine driving a generator. Heat is recovered from the engine, lubricating oil and exhaust gas cooling systems.
About 0.35 kWh of electrical energy and 0.55 kWh of useful heat can be obtained from a kilowatt-hour of fuel (Fig. 4). Hence a very effective exploitation of the energy endemic in the fuel is obtained. In the case of gas engines with exhaust gas catalyzers or lean-mixture engines, specific emission values are obtained which are lower than those of conventional gas-fired boiler installations.
A packaged heat-and-power station is made up of five modules. No particular civil engineering preparations or foundations are required for such a packaged heat-and-power station. The specific floor loading is only some 1000 [kg/m.sup.2]. The multi-cylinder engines function on an extremely lean mixture. Sound attenuating covers can be fitted to keep the noise level to a minimum possible.
The vapor compression system has proved itself to be technically and technologically suitable for use in connection with wort cooking. On the other hand, the packaged heat-and-power station can be used to advantage (from the energy economic performance aspect) for heating the wort from 74/75 to 100 degrees C. Here the packaged heat-and-power station has to provide 3.73 [kWh.sub.th] per hectoliter FW (Table 2).
For best possible heat transmission in a plate-type heat exchanger, the temperature difference has to be between 78 and 103 degrees C. The wort temperature range (74/75 degrees C. to 100 degrees C.) determines the hot water temperature difference of the cooling water from the packaged heat-and-power station. Moreover, this heat has to be available at short notice, i.e. within 15 to 30 minutes. This rapid availability is, however, only ensured when the heat can be called up from a heat accumulator. Provided that process water is still to be warmed up simultaneously, for example, 0.18 hl per hectoliter of FW from 15 to 75 degrees C. (heat requirement 1.28 [kWh.sub.th]/hl FW, follow-up heating to 85 degrees C. by means of steam), the total heat requirement becomes 3.73 + 1.28 = 5.01 [kWh.sub.th]/hl FW. Where the thermal utilization efficiency of the packaged heat-and-power station is about 55 percent, the primary energy requirement thus is about 9.1 [kWh.sub.th]/hl FW.
Nowadays, breweries require electricity amounting to about 8-11 kWh/hl RSB. Some 2.5 to 3 [kWh.sub.th]/hl RSB are taken up for refrigeration, whereby the cooling requirement is 9.3 to 11.6 [kWh.sub.th]/hl RSB. A further 2.5 t 3 [kWh.sub.el]/hl RSB are required by the bottling and cash filling sector. The remaining 3 to 5 [kWh.sub.el]/hl RSB are distributed round the production and energy supply sectors, together with general purposes. The electricity consumption for lighting is contained in this - 1 to 1.5 [kWh.sub.el]/hl RSB.
Some 35 percent of the primary thermal energy input of a packaged heat-and-power station can be obtained as electrical energy. With a primary input of 9.1 [kWh.sub.th]/hl FW, electricity amounting in quantity to 3.2 [kWh.sub.el]/hl FW or 3.5 [kWh.sub.el]/hl RSB can be generated. Since, however, the vapor compression plant itself requires 0.3 to 0.4 [kWh.sub.el]/hl FW, some 2.8 to 2.9 [kWh.sub.el]/hl FW or 3.1 to 3.2 [kWh.sub.el]/hl RSB are left for the remaining functions. Thus at least the total electricity consumption of the refrigeration plants can be covered.
Assuming that the packaged heat-an-power station specially designed to cope with the requirements of the wort heating up is only in operation when the brewhouse also is functioning, there is no problem involved in utilizing the electricity generated (about 3 kWh/hl RSB) also during this production time. It is fed directly into the plant electricity supply network.
Packaged Heat-and-Power Station
and Refrigeration Generation
It is certainly tempting to couple the packaged heat-and power station directly with a refrigerator compressor plant. This would be a way of avoiding generator and transmission losses. Figure 6 shows such a module schematically .
However, the packaged heat-and-power station should be installed in the brewhouse zone or in its vicinity, since it is here that the usable heat is required. The largest refrigeration consumers, the fermentation and storage cellars ("cold block"), are generally located at some considerable distance from the brewhouse ("warm block"). Hence, when the module generates all the refrigeration, the majority of same has to be transported into the cold block. A smaller part is required, moreover, in the filling sector (pressure tank or filter cellar), and possibly also for the short-duration heat up. The transport of this refrigeration causes considerable losses. Where the module supplies only electricity for the production of refrigeration, the energy required can be distributed to the electricity consumers easier and with lower overall losses. This applies particularly when due to the presence of different cooling requirements, the refrigeration installations are decentralized and, moreover, function at different evaporation temperatures.
It is first necessary to define the production conditions in the brewhouse before the packaged heat-and-power station can be dimensioned. Hence, for example, the "copper-full quantity" which is to be heated up is a basic item of necessary information, which again is established by the total evaporation rate during the cooking of the wort.
Nowadays, larger breweries mostly work continuously, operating three shifts in the brewhouse. Per day, six to eight brews (or multiples of same where multi-copper installations are operating) are made. Six brews per day means a brewing process lasting 4 h, eight per day, a duration of 3 h per process. After each of these periods of time, the necessary thermal energy to heat up the wort has to be available: in each case the charged-up heat accumulator is discharged in 15-30 minutes.
Here is an example. Where 3.73 [kWh.sub.th] per hectoliter of FW are required for 500 hl finished quantity, the packaged heat-and-power station has to provide a usable output of thermal energy to heat up the wort - i.e. 500 hl FW x3.73 [kWh.sub.th] per hectoliter of FW over a four-hour period (six brews per day)= 466 kWth. In the case of eight brews per day, the output has to be higher, i.e. 500 hl FW x3.73 [kWh.sub.th] per hectoliter FW over a three-hour period= 621 [kW.sub.th]. The corresponding mechanical packaged heat-and-power station output is, for six brews a day, about 409 [kW.sub.mech], and for eight brews a day 545 [kW.sub.mech]. The corresponding electrical generator outputs are 389 [kW.sub.el] or 518 [kW.sub.el] respectively.
Heat obtained from a vapor compression replaces primary heat energy for wort cooking, whereby some 10.11 [kWh.sub.th] per hectoliter RSB replace the heat produced by firing fuel. On the other hand, the vapor compression installation requires about 0.35 [kWh.sub.el] per hectoliter FW or 0.4 [kWh.sub.el] per hectoliter RSB.
The output from the block heating power station replaces primary energy to heat up the "copper-full" of wort, corresponding to 5.69 kWh per hectoliter RSB which has not to be obtained by burning fuel. The packaged heat-and-power station, requires, however, 9.1 [kWh.sub.th] per hectoliter FW or 10.1 [kWh.sub.th] per hectoliter RSB primary energy. The 3.5 [kWh.sub.el] per hectoliter RSB generated by the packaged heat-and-power station replace the equivalent amount of electricity from the public supply grid.
Table 3 summarizes the savings which are possible by combining vapor compression with the packaged heat-and-power station. Basing on natural gas with a lower calorific value of 10.0 [kWh.sub.th/m.sup.3] and an average price of 0.25 DM/[m.sup.3], as well as on average electricity costs of 0.20 DM/kWh, the combination of vapor compression and packaged heat-and-power station brings electricity savings of 0.1425 DM per hectoliter RSB respectively, i.e. a total of 0.7625 DM per hectoliter RSB. [Tabular Data Omitted]
Considerable quantities of carbon dioxide are formed by the combustion of primary energy carriers (table 4). Where, on the other hand, vapor compression and packaged heat-and-power stations are utilized, in the case under discussion, for example, about 4.6 kg [CO.sub.2] can be avoided per hectoliter RSB. The total production of all the breweries in the Federal republic of Germany amounts to some 90 million hectoliters RSB per year (source: German Federal Environmental Protection Office, Berlin). Were half this production to be accomplished, using the facilities mentioned above, then a decrease of more than 90,000 tons per year of carbon dioxide emission would be obtained. This would be a considerable contribution to environmental protection, since [CO.sub.2] is a major factor in the "greenhouse effect."
PHOTO : 1 Brewhouse - infusion mash process, four brews in 24 h.
PHOTO : 2 Brewhouse - two-mash process, six brews per day, with whirlpool - type wort copper.
PHOTO : 3 Vapour compression and packaged heat-and-power station in the brewhouse.
PHOTO : 4 Energy flow diagram of the packaged heat-and-power station.
PHOTO : 6 Module, consisting of generator, gas engine and refrigeration compressor.
|Printer friendly Cite/link Email Feedback|
|Title Annotation:||Small-Scale Brewing in America|
|Author:||Gantner, Egon; Plesch, Franz; Unterstein, Karl|
|Publication:||Modern Brewery Age|
|Date:||May 13, 1991|
|Previous Article:||Stout-hearted brew.|
|Next Article:||Draft beer - a microbrewer's headache?|