Category Archives: EuroSun2008-2

Comparison of System Concepts

To compare the solar fractions that are reached with and without a conventional storage tank, the ranges of solar fractions from both nomograms are shown in a single diagram in Figure 7.

image184

Because of the limited storage capacities of the concrete slab, significantly larger collector areas are necessary to reach the same high solar fractions as with a conventional storage tank. Therefore, the cost-to-benefit optimum for systems using the concrete slab as a heat store has been limited to a solar fraction of 30%. Please note that this is only an approximate value and depends strongly on the boundary conditions of each project.

3. Conclusions

Solar thermal energy is a good solution for space heating of industrial buildings if there is no or not enough waste heat available. When considering solar thermal energy for space heating of a factory building, the first steps should be to reduce the heat demand of the building by insulating the building and reducing infiltration losses (e. g. loading docks instead of open doors). The nomograms were developed to provide a means for rough dimensioning typical system configurations. A system concept with a water storage tank and a system concept using the concrete floor slab as storage medium were analyzed and described in detail. If the utilization ratio is high, the solar fractions that can be reached are similar for both system concepts. Solar fractions reached with systems without storage tank can even be higher compared to systems with storage tanks. High utilization ratio means that either one or both the collector area or the heat requirement is low. In these cases, the cheaper system concept without a storage tank makes a lot of sense. However, if the heat requirement is relatively large or if very high solar fractions should be reached, the system concept with a storage tank has an advantage. It should be noted that the option of having no storage tank and reaching a 100% solar fraction is feasible if an air temperature in the building that sometimes falls below the desired set value can be tolerated.

4. Acknowledgements

The presented work was performed as part of IEA-Solar Heating and Cooling and Solar Paces Task 33/IV “Solar heat for industrial processes”. The Austrian participation was financed by the Austrian Federal Ministry of Transport, Innovation and Technology.

References

[1] Klein, S. A. et al. (2005). TRNSYS, A Transient System Simulation Program — University of Wisconsin — Madison, Solar Energy Laboratory, Version 16.

Solar ORC without backup system

A preliminary assessment of the dimensioning of both solar field and storage system is based in the simulation results obtained for a system without backup energy. This assessment is based in two parameters: the capacity factor, CF (the ratio of annual values of mechanical energy produced by the solar cycle and the maximum mechanical energy that could be produced by the cycle operating continuously at full load), and the global solar to shaft power conversion efficiency, □ SORC, (the ratio of annual values of mechanical energy produced by the solar cycle and solar energy incident on the solar field) calculated with equations 2 and 3, respectively.

Подпись: (2)VT, annual

Wyj, x 24(^ / day) x 365(days / year)

Подпись: (3)

image241

VT, annual

Г SORC ~

KQcol, annual

The results obtained for both cycles at the three tested locations are presented in figure 3.

These results allow a parametric analysis of solar field area and storage time dimensioning, revealing the effect of storage time increase over solar to shaft power conversion efficiency results. For cycle 2, these results are more limited than those obtained for cycle 3, which reveal a wider range of storage capacity volumes leading to increased system efficiency.

The results presented in table 4 allow a comparison of the dimensioning of the system, at the three tested locations, after a reference condition of (CF = 0.3, maximum r/SORC).

Fig.3 — Capacity factor (CF) and solar to shaft power conversion efficiency (nSORC) results obtained for yearly
simulations of cycle 2 and 3 at Almeria (SP), Cairo (EGY) and Moura (PT)

Table 4. Solar field and storage capacity dimensioning for reference conditions of capacity factor CF = 0.3 and maximum global solar to shaft power conversion efficiency, rjSORC for cycles 2 and 3 at tested locations

CF

Almeria (SP)

Cairo (EGY)

Moura (PT)

SC [h]

Aa [m2]

Vsorc

SC [h]

Aa [m2]

Vsorc

SC [h]

Aa [m2]

Vsorc

C2

0.3

5.3

3140

4.4%

2.6

2430

5.0%

5.1

3110

4.4%

C3

0.3

5.1

1900

7.0%

2.2

1500

7.8%

4.4

1900

7.0%

Wort boiling — initial state and energy efficient alternatives

The wort boiling is the key process within a brewery. Because of the high thermal energy consumption and the high temperature level, two heat recovery systems that can cover the hot water demand of the whole brewhouse or even the whole brewery are usually installed.

Within the last 100 years, there has been a continuous development of the wort boiling process by the brewing industry. The main objective was to reduce the amount of water that has to be evaporated, which results in shorter boiling time and reduced energy demand. So it was possible to reduce the amount of evaporated water from more than 16% (equals a boiling time of more than 120 min) to 3..5% (35..50 min), while increasing the quality of the produced wort. At present, there are lots of boiling systems available that are offered by different companies. These systems differ mainly in the used boiling copper, its position within the brewhouse, the process control (continuous or batch), heat exchangers, pressure and temperature profiles as well as used heat recovery installations [9].

The wort boiling at the Hutt brewery takes place by so called classical internal boilers at atmospheric pressure. In the beginning, the wort is heated from 74°C to boiling temperature by indirect heating of the outer surface of the wort copper. After reaching the boiling temperature, the wort flows several times through an internal boiler that is placed directly in the copper. While passing the tube bundles of this boiler, the wort is heated under pressure to about 101..105°C.

While leaving these tubes, the wort starts to evaporate. Compared to the state of the art within wort boiling, this boiling system is relatively simple and old. It consumes a high amount of thermal energy, due to the required time and temperature for atmospheric boiling, the relatively high amount of water that has to be evaporated and the missing insulation of the boiling copper [10].

To clarify the operating mode of heat recovery installations within a brewery, figure 2 displays the initial state of the wort production at the Hutt brewery in a simplified way. Two hot water storage tanks, each 50 m3, are installed to cover the hot water demand of the whole production process, including filtration and bottle filling hall. These tanks are connected in serial and charged by two heat recovery installations. The first storage tank is fed by the heat exchanger within the process step of wort cooling and has a temperature level of maximally 80°C. The second store is fed by a tube bundle heat exchanger that condenses the vapours which occur during wort boiling. Two modes of operation can be chosen: heating cold brewing water to 80°C, or increasing the temperature of the already stored hot water. All consumers of the brewery are fed by the second storage tank with the higher temperature level. The main hot water load is caused by mashing (58°C) and lautering (78°C). Other consumers with lower hot water consumption are cleaning processes, sterilisation and keg filling. If process steps require lower temperatures than the storage tank temperature, the stored water is mixed with cold water. The consumed amount of water from store number two is settled by the first storage tank. An additional heating device that runs with steam ensures a set temperature of minimum 80°C in the upper part of storage tank number two during weekends or longer periods with no heat recovery.

image194

Fig. 2. Initial state in the brewhouse at Hutt brewery.

As mentioned before, there are multitude wort boiling systems available. These systems differ in the way of heating lauter wort and the used boiler. The overall objectives for this process step are to assure a gentle and rapid heating of lauter wort and gentle wort boiling with low shear forces. Further on, large evaporator surfaces, good circulation and mixing of wort and a limited but sufficient boiling time is requested [11]. Based on these and even more requirements, every brewhouse manufacturer has its own solution for the ideal wort boiling system. These can be classical internal or external boilers, thin-film evaporators, dynamic low-pressure boiling, high — temperature wort boiling, secondary evaporation under vacuum or downstream thin-film evaporation [10]. All of these systems vary a lot in the overall energy consumption, due to the boiling process as well as the heat recovery installations, which influences the water balance of the whole brewery.

Based on the relatively old and inefficient atmospheric wort boiling at the Hutt brewery, the technical management planned to implement one of these new boiling systems. During the planning phase, two different boiling systems were under consideration: a vacuum boiling system and dynamic low-pressure boiling. The vacuum boiling is characterised by a special geometry of installations and two boiling phases (atmospheric and vacuum) that are adjustable at will and cause a reduced evaporation. The whole boiling procedure takes place in a cycle consisting of a storage vessel, an external boiler (calandria) and an expansion evaporator in which a vacuum can be applied depending on the respective boiling mode. A tube bundle heat exchanger will be used to condense the vapours and pre-heat cold water. The main advantage of this boiling technology is the reduced effort for implement all installations in the existing brewing process. Besides savings of thermal energy, this boiling system shows an increased electricity demand for generation of
vacuum. The dynamic low-pressure boiling represents boiling at slight positive pressure with periodically increased and subsequently reduced pressure. An internal boiler is mostly used for heating and boiling. This boiling system is combined with a special heat recovery system that uses the condensation enthalpy of vapours to pre-heat the lauter wort. This heat recovery system consists of a common tube bundle condenser, special high temperature storage and an additional heat exchanger for the lauter wort [12].

Evaluation methodology and drying control

To establish solar kilns as an industrial tool, performance tests must be carried out during different season periods, based on objective data taken from measurement and analysis of several parameters. In this work, the inclusion of permanent measurement and control instrumentation has been adopted, which is an innovative aspect introduced for SECMAD project.

The main objective of the measurements and analysis is to characterize solar kiln performance, regarding operation time and costs under several weather conditions, as well as the related evolution of relevant physical quantities like: inside the kiln chamber, air circulating temperature and relative humidity and moisture contents (MC) of drying wood; at the solar collector zone, air temperature and relative humidity; air temperature and relative humidity on the outside environment;

Wood equilibrium moisture contents (EMC) in the interior and exterior of the kiln are also calculated from these measurements; as they are usual and useful drying indicators in the lumber sector that integrate the contribution of both temperature and relative humidity conditions. Additionally, energy expenditure, solar radiation and air convection can also be measured. Optimization of operational conditions to reduce drying time was considered and can be carried out automatically by the control instrumentation, where a dedicated fuzzy algorithm takes into account the restrictions imposed by quality issues and acts upon the ventilation system, presenting a flexible response to the natural change of exterior conditions (solar radiation, and psychometric conditions of external air, etc.).

Measurements and control can be taken at operator’s defined constant intervals that can lie in the range for one minute to several hours, with a usual value of 15 minutes. Instrumentation system also offers data logging and monitoring capabilities.

2 Results and discussion

A major problem with solar kilns is related with the uncontrollability of environment conditions and the difficulty to repeat them in consecutive drying operations. Therefore, all results are dependent on the specific weather conditions, besides of kiln structure, drying product and control strategy.

However, for similar weather conditions (solar radiation and relative humidity), some common evolution patterns have been noticed. Figures 3 and 4 represent one entire week evolution of temperatures and equilibrium moisture contents in the exterior and in the interior of a solar kiln charged, respectively, with moisture saturated wood and medium dried wood (MC ~ 30%). In both situations, there was sunny weather and the ventilation was switched on during the day period.

Data on these figures were acquired, respectively, during autumn and winter 2006 at INETI Lisbon facility — 38° 46’ N, 9°10’ W.

The efficiency of the kiln, illustrated by EMC values, is lower in the early hours of the morning, but increases with radiation intensity. As can be seen, EMC values present always less amplitude variation inside than outside the solar kiln. Although EMC values at the interior are higher during winter than in autumn, as expected, drying conditions can be quite favourable inside of the kiln during the winter period.

In spite of ventilation, chamber peak air temperatures (around midday) showed to be in the worst case 3-5°C higher than the outside ones. These small increments in temperature are sufficient to low relative humidity and EMC, in a significant way, causing these quantities to attain their lowest levels at this time and promoting wood moisture loss, in a more effective way. In fact, wood moisture loss increases with the decrease of relative humidity, mainly due to the increase of the water vapour pressure differential, which is the key factor for moisture evaporation. In this way, wood works as an additional moisture source inside the kiln, increasing RH and EMC. This effect is more intense if the wood is saturated as in the case of figure 3, where the chamber EMC values are bigger than the exterior ones (in opposite of figure 4, where wood has already attained 30% of moisture content), in spite of the ventilation.

If, in this case, exchange with the exterior is prevented, internal RH and EMC values would attain much bigger values. In such situations air has to be continuously expelled to the exterior and renovated at a high rate, forcing air circulation through the wood-stack.

—— Exterior EMC

Interior EMC

—— Interior Temperature

—— Exterior Temperature

Fig. 4 — Wood temperature and moisture equilibrium content inside and outside of the kiln,

December (winter), one wee

Figure 5 shows another typical evolution pattern of the equilibrium moisture content and temperature during a summer sunny day, both inside and outside the solar kiln, charged with saturated pine wood. Vertical lines correspond to the beginning and end of ventilation period, during which the ventilators were switched on and off.

Подпись: ш image254

It can be noticed, that even though the ventilation is on, during the hours of bigger incidence of solar rays, chamber temperature suffers a bigger increase than in autumn or winter, causing a bigger drop in the interior EMC values and offering better drying conditions

Fig. 5 — Typical summer day equilibrium moisture content and temperature
Evolution inside and outside the solar kiln

image255

Global results of an entire drying operation, during the end of autumn and the beginning of winter, using 27 mm thickness boards of pine wood, in a total wood volume of 40 m3, are illustrated in figure 6. Expelled moisture rate was increased by proper exposition of the wood boards to the air. The 40m3 volume of 27 mm thickness boards presented a total surface exposition (two faces for one board) of 3000 m2.

Fig. 6 — Drying process evolution of water loss (left) and moisture content (right).

In the first drying phase, high air circulation was provided, in order to speed as much as possible the drying rate. It should be emphasized that another important reason to quickly reduce wood moisture content at the initial stage, is to prevent the development of mould or blue stain specially when drying softwoods, namely pine. In the illustrated example, at the beginning of the process, an extraction of 75 liters of water per cubic meter was achieved (Figure 6). This represents a total water removal from wood in 24 hours about 3000 liters. This water removal rate dropped in seven days to about 35 liters per cubic meter and a value of 12 % in moisture content was reached in 33 days.

Figure 6 shows some other details of the final stage of the drying operation. Although temperature has not exceeded 30°C the wood moister content (MC) was reduced from 30 % to 15 % in only 7 days. This is quite significant, taking into account that the final drying stage is the slowest in a solar kiln. As can be seen, the EMC during this phase reached an average value of 9 % along the day when temperature increases and relative humidity was at its lowest (RH).

Monitoring data acquired during several runs under variable conditions, in all prototypes, allow the proposal of expected durations for the drying of softwood according to the different weather conditions. Table 1 summarizes the expected drying duration for different board thicknesses and favorable or less favorable conditions, based on the tests carried out during the project.

Table 1 — Expected solar kiln drying duration for softwood (Pinus pinaster, Aitim.), from 120% to 14% M. C.

Thickness

27 mm

35 mm

Total drying duration with favourable conditions (day)

15

25

Total drying duration with non favourable conditions (day)

45

60

Regarding energy, it must be said that the total amount needed to dry wood is the same whatever the method. For pine wood, the heat energy needed is about 494 kWh / m3. In conventional kilns, this energy is usually obtained from burning residues that can be quite cheap, but it must be remembered that the investment on a boiler is very high and the combustion produces CO2 emissions. In air or solar drying, the use of solar energy greatly reduces the expense and gas emissions. In the case of the present study, the kiln has a low cost structure and only energy spent in electrical ventilation has a cost per operation.

Table 2- Compared energy use in a solar kiln and a conventional kiln drier for softwood (Pinus pinaster, Aitim.), from 120% to 14% M. C. .

Electrical energy for ventilation per cubic meter

Heat energy per cubic meter

Conventional kiln drier

32 kWh / m3

460 000 kcal / m3 494 kWh / m3

Solar kiln drier

28 kWh / m3

3 Conclusions

The present work showed that low cost solar kilns can be competitively used to dry wood, presenting balanced benefits regarding operation time vs. final quality, energy expenditure and gas emissions.

A performance evaluation based on relevant physical quantities measurements and analysis is being carried on, during different season periods and weather conditions, constituting an essential tool to gather knowledge about the process. The results, documenting kiln functionality, strongly contribute to adjust the control to specific needs of products to be dried and to establish confidence in this kind of drying methods for industrial use.

As referred, in the first stage, wood drying requires a great capacity of water extraction, so strong ventilation should be carried, being necessary to extract the moisturized air from the kiln trough entire air renovations (1 to 3 per minute). In these circumstances, during sunny hours the gain in air temperature inside the kiln can be as small as 2 to 5 degrees. Although this apparently low increase

in temperature, the equilibrium moisture content can drop about 5 to 8 %, which is enough to dry wood at a very satisfying rate, even at its final stage.

Electric power reduction can be achieved through ventilation control, according to external conditions and drying level already obtained. It was found out that even forced air convection is always of great benefice, exchange with the exterior can be restricted, most of the time, to day hours (8h per day approximately).

A well designed structure and ventilation control strategy are the key factors for the economic success and drying quality. Even though drying times and energy expenditure have been acceptably low, more improvements can be eventually achieved.

One example is the possibility of allowing internal air recirculation in some circumstances, without exchange with external environment. This will account with another important ventilation effect, that wasn’t addressed in the present work, which is the removal of water vapor accumulated around the wood as a thin skin, whose presence diminishes the vapor pressure differential and favors the occurrence of mould blue stains that can affect final appearance and quality.

Combination of solar drying with conventional layout drying processes, including an adequate active control for optimization purposes, is another open possibility to achieve competitive substitution of fossil sources of energy, with significant decreasing of CO2 emissions, while still requiring low cost investments. Modifications of the industrial process are claimed to be minimal since the system requires no specialised buildings or electrical power, but should be clarified in furtherer works.

Acknowledgments — The information provided in this paper is a result of an applied research and demonstration project, partially financed by EU founds, and included in PRIME program, under the financial management of Innovation Portuguese Agency and managed by INETI.

References

[1] Ronald Voskens, Frank Zegers. 2005. Solar Drying in Europe. ECOFYS. IEA task 29.

[2] Maria J. Martins, Antonio Nogueira, Edgar Ataide, Sandra Enoch, David Loureiro, Arnaldo Cruz Costa, Alvaro Ramalho, Jose Santos, Luis Pestana. 2005. Monitoring and Control of an Energetically Efficient Wood Drying Process. EFITA Conference. UTAD. Vila Real.

[3] Titta, M.; Olkkonen, H., 2002. Electrical Impedance Spectroscopy Device for Measurement of Moisture Gradients I Woods”, Review of Scientific Instruments, Volume 73, N.8, August 2002, pp. 3093-3100.

[4] Steinmann, D. E., 1995. Real Time Simulation of Solar Kiln Drying of Timber. Solar Energy, Vol. 54,

N.5, pp.309-315

[5] Joly Patrice, More-Chevalier Francois, 1980. Theorie, pratique & economie du sechage des bois. Edition H. Vial., Durban

[6] Nogueira, A.., 2003. Estudo de estrategias de controlo para secador solar. XI Congresso Iberico e VI Iberoamericano de Energia Solar.

[7] Nogueira, A.., Ataide, E.., Martins, M. J.., Enoch, S., Loureiro, D.., Costa, A. C.., Santos, A.., 2005. Simulation and control strategies for an energetically efficient wood drying process. EFITTA /W CCA 2005 Joint Conference, Vila Real, Portugal, 25-28 July.

[8] Maria J. Martins, Antonio Nogueira, Edgar Ataide, Sandra Enoch, David Loureiro, Arnaldo Cruz Costa, Alvaro Ramalho, Jose Santos, Luis Pestana. 2005. Secador de Madeira Energeticamente Eficiente. Relatorio tecnico cientifico do projecto. INETI. Lisboa.

[9] Santos, J. A.; Martins, Maria J.; Costa, Arnaldo C.; Loureiro, D.; et al, investigadores Del INETI. 2006. Creada una camara de secado de costes bajos que reduce en dos terceras partes los consumos energeticos de un secador convencional. Comercio e Industria de la Madera (CIM) Editorial RBI, C/ Entenza 28 Entlo. 08015 Barcelona.

[10] M. N. Haque, et al. 2005. Assessment of the Actual Performance of an Industrial Solar Kiln for Drying Timber. Drying Technology, 23: 1541-1553. Copyright Q 2005 Taylor & Francis, Inc.

Components for Hybridisation

The channel burner model assumes a complete combustion. It evaluates the fuel consumption, the output mass flow and the composition of the exhaust gas by a given mass flow of air entering the

burner and a desired temperature. This burner model is used in the gas turbine as well. The gas turbine consists of a compressor, a burner, a turbine and a generator. Compressor and turbine are computing the resulting enthalpy and power consumption or production by using an inner efficiency. In addition, a pressure ratio can be set by the user.

Solar Cycle

The heliostat field model is based upon a simple field efficiency table interpolation dependent of the site, date and time. Only the total power to the receiver is calculated. The receiver outlet mass flow and temperature are calculated from the mass and energy balance and are dependent of the inlet conditions of the air flow and the concentrated radiation input.

Gas and steam properties can be integrated to each model. The different state variables are computed for Water and Steam by polynoms taken from the industry standard IAPWS-IF97 and for different gas mixtures by algorithms given in the VDI Guideline 4670 and provided by NASA.

Each model component created has the following advantages:

• is compatible to all others

• enables calculation for different site locations

• is applicable for different power plant sizes

• can be adjusted to different transport media: e. g. gas, exhaust gas

• easy modification

• can be used for short time scales down to minutes

High collector temperatures allow an all-season application and provide confidence with which one can plan

Every planner and user is interested in an efficient all-season application of the solar collector system. The performance of low temperature collectors drops considerably with falling outside temperatures. In winter or with not optimal weather they can never achieve much more than a preheating.

If heat is needed at different levels at the same time, e. g. for heating and hot water supply, the simplest solution is to provide and storage it at the highest level i. e. with the highest thermodynamic value. This is impossible with low temperature collectors, what leads to higher planning efforts and much more complicated hydraulic systems.

The missing of the predicted energy harvest with most of the large-scale projects with low temperature collectors was always explained by higher return-flow temperatures than planned. In fact, the return-flow temperatures are never the problem but the collectors itself because they lose substantial performance under real working conditions.

A SAHP Desalination System

The system consists of two main parts, a solar assisted heat pump, with refrigerant as its working fluid, and a water desalination section with preheats, as shown in Figure 1.

The solar assisted heat pump provides heating and cooling to the desalination process, with a serpentine tube solar evaporator collector that absorbs solar radiation and ambient energy. Refrigerant R134a is used as the heat pump’s working fluid. The serpentine tube, with 9.52 mm diameter was soldered at the back of the absorber plate. The bottom of the collector was insulated with polyurethane material. An open type reciprocating compressor, directly coupled to a three phase induction motor was used in the system. A frequency inverter controls the speed of the motor. Refrigerant passes through condenser coil, located at the bottom of the desalination chamber. To ensure complete condensation of the refrigerant, it is allowed to pass through a 250 l

[4] LEP: (Liquid Entry Pressure) if the feed pressure is higher than the LEP, then the liquid penetrates the membrane pores and the hydrophobicity is lost [8]. The LEP depends on many factors, but the main one is the membrane pore size, logically the bigger the pore size is, the smaller the LEP is and so is the working pressure.

[5] In the case of C3, the optimal cycle parameters correspond to evaporation at critical conditions.

Considering the stability of ORC operation, the maximum allowed evaporation temperature was bounded, in this analysis, to a value of 145 °C, 9 °C bellow the fluid critical temperature.

Solar Heat for Industrial Processes. Operating Plants and Potential for Application

R. Battisti1*, S. Drigo2 and C. Vannoni2

1 Ambiente Italia, Via Vicenza, 5/a 00185 Roma, Italy

2 University of Rome “SAPIENZA”, Department of Mechanical and Aeronautical Engineering,

Via Eudossiana, 18 00184 Roma, Italy

* Corresponding Author, riccardo. battisti@ambienteitalia. it
Abstract

The majority of the solar thermal plants operating today provide hot water to households, for both sanitary purposes and space heating. Although the residential sector offers a huge potential for solar thermal applications, the industrial sector should not be ignored for two key reasons.

First, this sector shows a remarkable relevance, covering about 28% of the total primary energy consumption for final uses in EU25.

Second, a significant share of the heat consumed in the industrial sector is in the low and medium temperature range. About 30% of the total industrial heat demand is required at temperatures below 100 °C and 57% at temperatures below 400 °C. The areas of application with the most suitable industrial processes include cleaning, drying, evaporation and distillation, blanching, pasteurisation, sterilisation, cooking, degreasing and surface treatment.

These two issues make the industrial sector a promising and suitable application for solar thermal energy.

In the paper, both the results of the analysis of the existing solar thermal plants for process heat and the assessment of the application potential will be described. Both activities have been carried out in the framework of IEA SHC and SolarPaces Task 33/IV.

Keywords: Solar Thermal, Industrial, Potential, Process Heat

1. Introduction

Considering the new applications for solar thermal, the industrial process heat at low and medium temperature up to 250 °C is one of the most promising. Industrial sectors such as food, wine and beverage, textile, transport equipment (e. g. car washing), surface treatment (e. g. galvanic) and the chemical require process heat in this temperature range. The areas of application are numerous and include different processes such as cleaning, drying, evaporation and distillation, blanching, pasteurisation, sterilisation, cooking, degreasing and surface treatment. In addition, several built examples showed that space heating of factory buildings has to be considered one of the most promising applications of solar thermal in industry.

A survey on the existing solar thermal plants for industrial process heat (SHIP, Solar Thermal for Industrial Applications) and a review of the potential studies for future applications have been

performed in the framework of the IEA Solar Heating and Cooling Programme and SolarPaces Task 33/IV: the results are summarised in the present paper.

At the end of 2006, the installed solar thermal capacity worldwide [1] was about 118 GWth (168 million m2). Compared with 144 GWel for wind and 5,5 GWel for photovoltaic, solar thermal is helding a leading position among renewables. The majority of the solar thermal plants operating today provide hot water to households. Although the residential sector offers a huge potential for solar thermal applications, the industrial sector should not be ignored for two key reasons.

First, this sector shows a remarkable relevance, covering about 28% of the total primary energy consumption for final uses in EU25 [2]. Second, a significant share of the heat consumed in the industrial sector is in the low and medium temperature range. These two issues make the industrial sector a promising and suitable application for solar thermal energy.

Solar ORC with thermal energy storage and backup

As well as the energy storage, the use of conventional energy backup for a 24 hour demand of mechanical energy is also considered in this paper. In that case, the annual solar fraction, SF, (the ratio of solar heat to total heat delivered to the cycle) is the characteristic parameter of the performance of the system.

Together with the specific power production, SP, (the ratio of annual mechanical energy produced and solar field area), this analysis opens way for a future economical analysis of the system, after adequate cost information for solar field, storage system and backup energy. The results obtained for both cycles at the three tested locations are in figure 4.

The results presented in table 5 allow a comparison of the system, at the three tested locations, using a reference condition of (SC = 6 h, SP = 300 kWh. year/m2).

Fig.4 — Solar fraction (SF) and specific production (SP) results obtained for yearly simulations of cycle 2 and

3 at Almeria (SP), Cairo (EGY) and Moura (PT)

Table 5. Solar fraction and solar field dimensioning for reference conditions of (SC = 6 h, SP = 300 kWh. year/m2) for cycles 2 and 3 at tested locations

SC

SP

Almeria (SP)

Cairo (EGY)

Moura (PT)

[h]

[kWh. year/m2]

SF

Aa [m2]

SF

Aa [m2]

SF

Aa [m2]

C2

6

300

0.29

2940

0.37

2940

0.29

2940

C3

6

300

0.37

2940

0.47

2940

0.38

2940

5. Conclusions

Project POWERSOL [1] aims at the development of a small scale solar thermal based mechanical power/electricity generator, suitable for applications with lower requirements of maintenance and operation expertise, as those found in industry, desalination or small communities.

In the present article, a performance analysis of such a power system at three different locations and at two different working temperatures is presented, allowing a preliminary assessment of its design.

Simulation of the system working without backup energy allowed the determination of the critical storage system dimensioning, as well as a preliminary (and conservative, in view of the simplified simulation conditions) estimation of overall system efficiencies, which present values, at the best location tested, of 5.0% and 7.8% for the lower (C2) and higher (C3) temperature cycles, respectively.

Further development of the project, allowing a better cost/performance estimation for the different solar thermal collector technologies addressing the cycles operating temperatures, will enable a

final economical analysis of the system, following the approach of solar fraction and specific

power production estimation presented in this paper.

References

[1] — “POWERSOL — Mechanical Power Generation based on Solar Thermodynamic Engines”, co-funded by the EC [Contract No. 032344 (INCO)], https://www. psa. es/webeng/projects/joomla/powersol/index. php

[2] Larson, D. L. (1987). Performance of the Coolidge Solar Thermal Electric Power Plant. Journal of Solar Energy Engineering, vol. 109, p. 2-8.

[3] Stine, W. B.; M. Geyer. “Power Cycles for Electricity Generation”. In: Power from the Sun. 2001. <http://www. powerfromthesun. net/chapter12/Chapter12new. htm>. [Last checked: 19th February 2008].

[4] S. Canada, G. Cohen, R. Cable, D. Brosseau, and H. Price (2004). Parabolic Trough Organic Rankine Cycle Solar Power Plant. DOE Solar Energy Technologies. Program Review Meeting. October 25-28, 2004. Denver, Colorado.

[5] Angelino, G.; M. Gaia; E. Macchi (1984). A review of Italian activity in the field of Organic Rankine Cycles. 1984. Proceedings of the International VDI-Seminar. Zurich, 10th-12th September.

[6] Garcia-Rodriguez, L.; Blanco-Galvez, J (2007). Solar-heated Rankine cycles for water and electricity production: POWERSOL project. Desalination 212 311-318

[7] Blanco-Galvez, J., Garcia-Rodriguez, L. Delgado-Torres, A. M., Alarcon-Padilla, D. C., Vincent, M. Organic (2008). Rankine Cycle driven by parabolic trough solar collectors: pilot test facility at the Plataforma Solar de Almeria. Las vegas2008

[8] Delgado-Torres, A. M (2007). Definition of thermodynamic boundary conditions (cycle 3). Technical Report POWERSOL-T220-02(a).

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Integration of Solar Heating System

Although breweries show a high heat demand at a low temperature level, it is relatively difficult to estimate in the first instance, if a solar heating system can be reasonable integrated into the existing processes. This is based on the diversity and complexity of the brewing process, as explained before. The basis for this decision is the detailed knowledge of the water — and energy balance of the overall production process. Some breweries don’t have any noteworthy hot water consumers beside the brewhouse, which can even lead to a surplus of hot water gained by heat recovery. In this case, the hot water is drained to the sewer and a non-concentrating solar heating system cannot be installed reasonably. Some breweries have several other hot water consumers beside the brewhouse, and need to produce the missing amount of hot water via conventional ways. And finally, hot water consumption and hot water generation can be balanced. If a change in the boiling system is planned, a new water — and energy balance has to be drawn, because of the interaction of boiling system and heat recovery. This might be difficult, since not all details are clarified before the new process is running. The link between boiling system, heat recovery and solar heating system and the associated changes in water — and energy balance shall be clarified in the following by the two considered boiling system at Hutt brewery.

image195The dynamic low-pressure boiling affects the water balance in a significant way.

The energy of evaporated water during boiling is directly used for the closed heat recovery cycle with a high temperature level and no longer to generate hot water. The only remaining source of hot water is wort cooling, which can supply the amount for mashing and lautering. In this case, the missing hot water demand can be suitable met with a solar heating system.

Together with the recovered heat from boiling that is used to heat the lauter wort,

high energy savings can be pig. 3. Possible integration of solar heating system in combination

achieved. with dynamic low-pressure boiling.

Подпись: The integration of the solar heating system into the brewing process after implementation of the vacuum boiling system is displayed in figure 4. In this case, the storage tank with higher temperature level would be fed by the heat recovery installation for wort cooling and the one with lower temperature level by the solar heating system. To ensure the required temperature for all process steps, the auxiliary heating system should be connected to both tanks. Additionally, the heat recovery during boiling can be used to increase the temperature level of both storage tanks. image197

image198The vacuum boiling system affects the heat recovery during wort boiling and wort cooling, but with lower effect. In case of wort boiling, the amount of recovered heat decreases by two reasons: the amount of evaporated water is reduced by at least 25% and approximately two third of overall evaporation is realised under vacuum. Beside the reduced amount of evaporated water, the boiling temperature during the vacuum evaporation phase is decreased successively from 100°C to 85°C. This leads to a reduced amount of energy that can be recovered. As a result of the lower temperature during vacuum boiling phase, the wort temperature prior to wort cooling is also lower compared to the old reference boiling system. However, a detailed knowledge of all process parameters in prior is not possible, since the brewer has to adjust the new boiling system to the specific requirements, which influence the final boiling temperature and ratio of atmospheric to vacuum boiling phase. Nevertheless, both heat recovery installations are here used to heat water, which leads to an amount that should be adequate to cover the overall hot water demand of the brewery. If the actual water balance in a brewery is already balanced, an implementation of a solar heating system is rather difficult after this retrofit. To find a suitable way for the implementation in combination with this vacuum boiling system, a change in the heat recovery during wort boiling is required. In this case the condensation enthalpy should not be used to generate hot water, but to increase the temperature of the already stored water. Likewise, the storage concept should consider the separation of high and low temperature level as shown in figure 3.

2. Conclusion

This paper showed the large diversity in the brewing sector, especially within the process steps of wort production. Although breweries generally show a high thermal energy demand at a relatively low temperature level, a reasonable integration of solar heating systems can be rather difficult. This is based on various technical installations that are available and a high rate of heat recovery, which can also vary a lot by means of temperature level and used installations. There is no general approach to implement a solar heating system in breweries so far. It will probably always be essential to draw a detailed water and energy balance of the overall production process for every single brewery. This balance should include all accumulating hot water streams with the respective temperature level. If there will be a change in the technical installations that influences the produced and/or consumed hot water, a new balance has to be drawn. Based on this balance it has to be proven, if a solar heating system can be integrated in the existing process or not. Furthermore, the integration can be difficult, if the complete heat recovery runs at lower temperature levels to produce hot water.

3. Acknowledgements

The authors gratefully acknowledge the financial support provided by the Reiner-Lemoine-Stiftung and the German Federal Ministry for Environment, Nature Conservation and Nuclear Safety, contract No. 0329601T. Additionally, we would like to thank the Hutt brewery (esp. K.-P. Reinl) and GEA Huppmann (esp. Dr. L. Scheller) for the close collaboration within this research project.

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