Solar Process Heat for Industrial Processes

Cedro Exchange Issue Number 9 - December 2013

Guest Author; Martin Haagen, Business Development, Industrial Solar GmbH, Emmy-Noether-Str.2, 79110 Freiburg, Germany; martin.haagen@industrial-solar.de

IntroductionIndustry is responsible for around one-third of the total energy demand (Figure 1). This reality does not only cause a release of a significant amount of CO2, but it is also a substantial cost factor. According to a UNEP study (UNEP, 2011), industrial production is expected to grow by a factor of four by 2050. Thus, as fuel prices continue to rise, industrial energy supply ultimately also effects competitiveness of countries and industries.

The major share of industrial energy demand is pertained to heat for industrial processes (Figure 1), which can be further differentiated by temperatures (Figure 1). A large share of the energy demand for low and medium temperatures can be covered by solar collectors. Thus, solar process heat not only reduces CO2 emissions but also reduces the production costs and thereby contributes to the relative competitiveness of producers.

Figure 1: Energy demands and Process heat temperatures

Fischer Eco Solutions GmbH Germany

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The total industrial energy consumption in Lebanon was 6.2 TWh in 2010 (IEA 2013) and similar patterns as in Figure 1 can be assumed. Since Lebanon imports almost its entire energy supply, the application of solar process heat would undoubtedly free resources from energy imports towards other and more productive uses.

2 - Suitable Sectors

Almost all industries have a thermal energy demand. Some exemplary sectors are shown in the Table 1 below.

3 - Solar thermal collectors

There are numerous solar thermal collector technologies available. A major distinction can be made between non-concentrating (see: CEDRO Exchange 7) collectors and concentrating collectors (see: CEDRO Exchange 8).

The major different solar thermal collectors’ technologies will be briefly described in

consideration for solar process heat. An overview is shown in Figure 2 below.

Flat plate collectors are the most straight forward solar thermal collector technology. Water circulates through pipes in an isolated box covered by glass to reduce heat losses.

In vacuum tube collectors water circulates through pipes which are placed in vacuum glass tubes. Thereby heat losses are further reduced and higher temperatures can be provided more efficiently compared to flat plate collectors.

In concentrating reflectors, like the Fresnel collector or parabolic trough collectors, the irradiation first falls on reflective surfaces from which it is reflected and concentrated onto an absorber. Thereby very high temperatures of more than 400°C can be achieved. As the sun moves over the day and over the year concentrating collectors continually track the sun. Below (Figure 3) the functioning principle of a Fresnel collector is shown. Direct irradiation falls onto the slightly curved primary mirrors. These mirrors track the sunlight uniaxially over the day and concentrate the sunlight onto the absorber tube. A heat transfer fluid (pressurized water, steam or thermal oil) circulates through the absorber and provides thermal energy to the process.

Table 1: Overview of selected industrial processes suitable for application of solar process heat

Figure 2: Overview of selected solar thermal collectors

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Figure 3: Function Principle of Fresnel Collector (Copyright: Industrial Solar GmbH)

Figure 4: Direct Normal Irradiation for Lebanon (source: http://www.solar-med-atlas.org)

Other concentrating collectors, like the parabolic trough collector, operate with a similar principle. A further distinction has to be made in reference to the irradiation.

While flat plate collectors and vacuum tube collectors can use direct and diffuse irradiation, concentrating collectors only work with direct irradiation.

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Figure 5: Integration of Solar Process Heat

As shown in above (Figure 4) Lebanon has very good direct irradiation and is therefore well suited for the application of concentrating solar collectors. For them to be applicable in industries there are specific demands which differ from domestic application or solar power plants (CSP plants).

4 - Key criteria for the selection of solar process heat collectors

The following aspects are especially relevant aspects to be considered when identifying the optimal solar thermal collector technology.

Space efficiency

Solar energy is abundantly available. However, for the collection of solar energy comparatively large areas are needed. At the same time industry is extremely energy intensive and

empty unused space in industrial areas is scarce. Thus, for solar process heat, the solar collector technology should have high ground space efficiency and allow roof top installations.

Temperature control

Industrial processes today are often very sensitive to variations in temperature. Thus, it is important that solar collector systems provide accurate temperatures according to the specific demand.

Integration

Most industries use steam as a heat carrier which supplies heat to different processes. Solar process heat systems are integrated in conventional heating systems to reduce fuel consumption while availability is guaranteed. There are three ways to integrate thermal energy as shown (in Figure 5) below.

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1. Pre-heating of boiler feed water is the simplest method. However, as most energy is needed for evaporation only a minor share can be integrated. Moreover, when the condensate returns at a high temperature the efficiency of non-concentrating collectors is reduced.

2. Integration on the distribution level allows a large solar share. However, as high temperatures (mostly steam) are needed only concentrating collectors can be used. Integration on the distribution level provides the greatest flexibility as it is not linked to a specific process which might not run continuously.

3. Direct coupling with a specific process is another way to integrate solar thermal energy. However, when the process is stopped or changed, it can be challenging to make use of the energy. Thus, this approach is rather inflexible.

5 - Solar thermal market in Lebanon

The market for solar thermal collectors in Lebanon is dominated by low temperature collectors for domestic applications. Today most of the newly installed collectors are imported, mainly from China and Turkey. The market is continuously growing due to rising

Table 2: Export of selected Lebanese industrial sectors in 2012 (source: Ministry of Industry, Statistical reports, December 2012)

energy prices; but is still less developed compared to neighboring countries. There are no installations with high temperature collectors.

6 - Potential for Solar Thermal Process Heat in Lebanon

Increasing fuel prices are a heavy burden for industries in Lebanon. Moreover, as electricity is not continuously supplied, most industries have their own equipment to generate electricity, which further raises their demand and associated costs for/of fossil fuels. Thus solar thermal processes for the industrial sector, including solar cooling (see below), are interesting opportunities that would reduce electricity consumption. According to a study by the Ministry of Industry the total expenditures for energy (electricity and fossil fuels) accounted to 8.1% of intermediate consumption. Most of the large industries are located in the governorates of “Mount Lebanon” and “Bekaa” where there is good irradiation. The most suitable sectors in Lebanon are the food sector, the chemical sector. As well as the paper sectors as they account for a large share of the exports (Table 2) and have suitable processes as shown above (Table 1). At the same time the sectors offer various possibilities to integrate solar thermal energy in their processes.

Moreover, where grids are weak such as in Lebanon, less backup power has to be reserved to power the chillers.

Solar thermal cooling is not only interesting for air-conditioning but also for industries. The food industry has a constant cooling demand for their storages. Other industries need to cool their machines during operation.

7 - Solar Cooling

Apart from the direct use, the heat can also be used to power absorption chillers and thereby provide cooling. Absorption chillers make use of different thermodynamic properties of fluids to provide cold. The driving force is heat; and electricity is only needed for pumps. Thus, expensive electricity can be replaced.

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fuel costs (e.g. price of heavy fuel oil) are a major factor for the financial viability of a solar process heat project. However, when fuel is not constantly available, the costs are not only reduced by process heat systems, but security of energy supply is also enhanced. Other major factors which impact the economics of solar heat systems are solar irradiation as well as investment and financing costs.

9 - Typical project in Lebanon

Based on the above, Table 3 below summarizes how a project in Lebanon could turn out.

Table 3: Economic Assessment of exemplary Solar Process Heat System in Lebanon

Figure 6: Solar driven cold store in Umkirch, Germany (Source: Kramer GmbH, Industrial Solar GmbH)

There are already solar driven cold stores. In Umkirch, Germany, Fresnel collectors provide heat to a single-effect absorption chiller, which produces cold. The cold is either used directly to cool the cold room or to charge an ice-storage. Thereby the system can even overcome times without irradiation.

8 - Economics

Solar process heat systems reduce the fuel demand of industries and the associated savings cover the investment costs. Thus, the

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References

• ALMEE (2011); “Solar thermal market in Lebanon”

• CEDRO (2012); Exchange Issue Number 7; “Concentrated Solar Power Plants”

• CEDRO (2012); Exchange Issue Number 8; “High Rise Buildings and Solar Water Heater Installations”

• IEA (2013); Lebanese Energy Balances for 2010 http://www.iea.org/statistics/statisticssearch/report/?country=LEBANON&product=balances&year=2010

• Lebanese Ministry of Industry; Statistics http://www.industry.gov.lb/IndustrialStatistics/Pages/Statisticalreports.aspx and http://www.industry.gov.lb/Arabic/Arabic/IndustrialStatistics/Documents/Reports/Decembre%202012.pdf

• Lebanese Ministry of Industry (2010); “The Lebanese Industrial Sector, Facts and Findings 2007”.

• UNEP (2011); “Renewable Energy in Industrial Applications - An assessment of the 2050 potential”.

• Cover photo. copyright: Fischer Eco Solutions GmbH Germany.

Conclusion

For Lebanon’s industrial sector, energy supply becomes an increasing challenge as fuel prices continue to rise and power supply is not always guaranteed. Due to high irradiation, solar process heat is a viable option to reduce energy costs especially for the food, chemical and paper sectors. Solar process heat projects are economically viable; however, initial support might be needed since the concept is new to Lebanon. On a macro scale, solar process heat reduces not only the import of fossil fuel, but can create employment due to the local added value.