The integration of solar energy into an industrial process requires studying and analyzing the existing heat supply system and determining the potential energy savings and the energy flows and temperatures levels of the process.
In most factories, the central system for heat supply is working with hot water or steam at a pressure corresponding to the highest temperature needed among the different processes.
Possibilities for the coupling of the solar system with the conventional heat supply
Solar thermal energy feeding into the existing hot water system
The integration of solar thermal heat into industrial processes can also be done by integrating the solar heat directly into the existing heating system. Such integration requires that the solar collector operates at the same temperature than the existing heating system.
Feeding of solar heat to the process equipment directly
Integrating solar system in the conventional heat system is to integrate it directly in the process heat.This implies to integrate another heat transfer in the production area if the temperature from solar system differs from the temperature coming from the heating medium. In this configuration, the efficiency of the solar collector can be boosted when the temperature of the process is close to the temperature from the solar collector.
Industrial solar systems without storage
In a lot of industries, the implementation of solar system does not require a storage system as the heat needed is higher than the heat provided by the solar system. This could happen when the process requires a continuous operation and/or a load always higher than the supply of heat by the solar system. In this case, the installation of solar energy system remains low cost, avoiding high storage related costs. In such configuration, the solar heat will be fed directly to the process or to the already existing heat supply, above figure is representing a system which needs a heat exchange as work fluid of solar system is a special fluid to protect the collector from freezing and corrosion.
Industrial solar systems with storage
Most industrial processes do not operate in a continuous mode over time, being ticked over at some time with strong fluctuation of the process heat demand during the operational periods. In these cases, a storage tank can be coupled to the solar system, which will store the unused solar energy collected during the operating-breaks (week-ends, short break of operation…) and will restore this energy collected to the process system during the working process periods.
Combination of solar thermal system and waste heat recovery
The integration of solar energy systems has to be thought within an approach which takes into consideration energy efficiency measures of which the waste heat recovery is one of the main measures. Thus solar heat should be introduced after a first preheating by waste heat recovery systems, and not as an alternative to these systems. Even if waste heat recovery raises the working temperature in the solar system, the combination of both systems yields better results than a solar system at lower temperature without heat recovery.
Contank plant (Parking Service Castellbisbal S.A., Castellbisbal (Barcelona), Spain)
The basic target for the solar thermal installation is the cleaning of containers used to transport liquid goods by rail. The main heat-consuming process in the company is the washing process of the containers, which needs hot water at 70 – 80 ºC (approx. 46% of the total heat requirement) and steam (the remaining 54%). The hot water required is in a range of 70 – 80 m3/day. In addition to the solar system, there is a gas-fired steam boiler for the preparation of hot water.
The solar thermal system installed is composed of two solar fields with flat-plate collectors of around 500 m², representing a total installed capacity of 357 kWth, and by a storage system of 45 m3. A steam boiler functioning with natural gas has been installed as back-up.
Keminova Italiana s.r.l. cosmetic plant in Brescia, Italy
The installation of the solar thermal plant in Keminova Italiana s.r.l company is for pre-heating of working fluids, heating of emulsions and factory building heating. The solar field is composed by 90 m² of flat-plate collector with a total capacity of 63 kWth. In addition, heat storage has been installed with a tank capacity of about 5 m3. The back-up system is the existing natural gas fired boilers.
The Misr-Helwan textile project – Egypt:
The project implemented three subsystems which were the solar water heating system, the waste heat recovery system and a meteorological data acquisition system.
The solar system was also composed of 350 m² of locally manufactured flat-plate collectors producing 26 m3/day of hot water at 50-60°C. The waste heat recovery system was waste heat exchanger in order to recovery the hot water being discharged to drain and to be used in the bleaching process.
The total system allowed saving 1,500 toe/year (around 30% of the total energy consumption of the plant) and 8,500 tCO2/year.
The El Nasr Pharmaceutical factory – Egypt:
The plant is made of 144 parabolic trough collectors (6 metres long by 2.3 metres wide) with a net reflective surface area of 1,900 m². The reflectors have been locally built and installed. The solar field is organised into 4 identical loops, each loops composed by 6 collectors’ groups of 6 parabolic trough collectors.
This application was in operation since 2003, the plant produces around 1.3 t/hr of steam saturated at 175°C and 8 bar equivalent to 0.9 MWth to feed the steam network of the company, thereby reducing the fuel consumption.
The solar-heated condensate is collected into a condensate tank return to the flash drum at about 23 bar. As the pressure inside the flash drum is kept at some 7.5 bar, flash steam is generated due to the sudden pressure drop. The installation of the solar system allowed replacing seven old mazout burners by dual burners suitable for mazout and natural gas with installation of automatic control system.
The total system allows saving 1,200 toe/year (around 30% of the total energy consumption of the plant) and 3,500 tCO2/year.
A dairy factory in Russeifa, Jordan:
The total solar field is composed of 96 flat-plate collectors,of 1.3 m² each one representing 128 sq.mt with a storage tank of 5 cu.mt. The solar heating of water was an improvement to the process of dissolving powder milk that produces reconstituted milk. Cold water was used for this process; however, in order to reduce the process time and consequently to reduce electrical power consumption of blenders, hot water quality of 40° – 50°C temperature is needed. The hot water is also needed for container washing purposes with water quality of 60°C.
Successful stories of Solar Thermal Industrial Applications in India:
GFCL – Andhra Pradesh:
- Working since 1997
- GHG emissions saved 22 GJ per day
- Capacity: 1,20,000lit/day
- Application:Boiler feed water pre-heating
Chelsea Textile Mills – Gurgaon:
Location: Sector -3, IMT Manesar, Gurgaon
Installed year:2006(successfully running till now)
Technology: Hybrid Solar Water Heater for Process Heating Application
size of system: 50,000LPD
For a typical application of parabolic trough – cost 40,000INR per sq.mts
Currently 5,400INR per sq.mts of reflective surface subsidy from MNRE and 80% accelerated depreciation in the first year can recover almost 50% of the systems cost.