**3. Solar thermal technology application in post combustion CCS on a thermal power plant**

Concentrated Solar Plant (CSP) is presently a matured technology in which several thermal energy storage options are being deployed. Energy storage in form of heat offers a potential pathway for small (local) and large (utility power plants) scale applications. Thermal storage systems provide a unique opportunity to store energy locally in the form of heat that cannot be transported over long distances. Current thermal storage systems are still in its infancy. The most common ones are large, water-heating storage tanks and molten salt-based systems at solar power plants. These systems have been designed based on the economics of water and salt, the heat capacity of water, and the latent heat of salts. Research on a large host of sensible heat storage and phase-change materials have been conducted over the past two decades. The materials parameters that are relevant for this application are: melting point, boiling point, vapor pressure, density, heat capacity, thermal conductivity, latent heat of fusion and chemical reactivity. While it is intuitive that increasing the temperature of storage could pack in more energy, barriers to the development and deployment of high energy density storage remain, including handling materials at high temperatures, associated systems costs, and operating costs. Thus sensible thermal storage systems are cost prohibitive. Phase change materials (PCM) do provide a viable economical solution for higher energy storage density. However, operation temperatures limit current PCM systems; higher temperatures cause chemical instability and reactivity with containers. Development of affordable high-density thermal storage system will only be possible by utilizing low cost earth abundant thermal storage materials in conjunction with suitable thermally insulating container materials. Current heat storage systems utilize either sensible heat storage (i.e. water in storage tanks) or latent heat storage (i.e. phase-change materials such as molten salts). The relatively low operating temperatures of these systems limit their capacity to store thermal energy; storage systems with higher temperatures would be more economical.

1000°C [14, 15]. The unique aspects of this system are the selection of an alkali halide salt with high melting temperature and a corrosion resistant cheap ceramic container material. The thermal storage unit will be coupled with a high solar concentrator system (1000–10,000×). As a part of an on-going project at RKDF University in near vicinity of RGPV, funded by MNRE, the project collaborator in Solar thermal, the Rensselaer Polytechnic Institute of USA has developed flux grown crystals of high melting temperature (700–1500°C) mixed alkali halide compounds doped with metallic impurities to enhance thermal conductivity. The trade-off between material density, specific heat capacity, thermal conductivity and cost of raw material has been evaluated to develop a material system that could meet the system's specification at cost of energy storage lower than current electrochemical systems (batteries). In addition, a SiC based composite polymeric coating solution has been developed to avoid corrosion of steel containers used for the thermal storage unit [16]. These materials have been shipped to RKDF University and incorporated into the field unit (test-bed). The test-bed at RKDF comprises of a thermal storage unit, Fresnel lens based solar tracking unit to focus sunlight into the thermal storage media and a steam generation unit (for future electricity generation using a steam turbine). **Figure 5** shows the installation and initial evaluation activities of

An Innovative Approach in Post Combustion Carbon Capture and Sequestration…

The expected physical outcomes of the project of CSP integration with CCS as discussed above

thermal power station for future development of technology of CCS in India and countries

Test results have shown that the innovative halide salt used as thermal storage material stores heat to such an extent that it retains heat for over 5 days to be able to produce steam (**Figure 6**). This innovative halide salt was also tested in the pilot plant shown at **Figure 5**. The biggest challenge in this project is, however, the development of Alkali Halide Salt indigenously for which efforts are under way at RKDF University to procure some of the key components for growing crystals with high energy density, capable of retaining heat. Also efforts are underway towards indigenous development of Heliostats, Fresnel lens

between tropic of cancer & capricorn bestowed with high solar DNI [1, 7].

capture and sequestration on an actual

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103

the solar thermal storage unit at RKDF University.

are in terms of establishment of the pilot plant of CO2

and low cost trackers.

**Figure 5.** Solar thermal storage unit at RKDF University.

The technologies which hold promise for achieving temperatures in the range of 150–600°C and beyond can be categorized by the phases of matter of the materials used: liquid, gaseous, solid, as under:


In this CCS integrated with CSP project we examined several options of 'Solid Pathway' such as cast iron core of Mount Abu 1 MW solar plant used for steam generation, CL-CSP plant at the State technological University of MP, RGPV, in Central India in which pebbles/rock storage has been proposed for energy storage for heating air in primary cycle and steam in secondary cycle.

In this CSP to CCS integration project, we are developing an affordable high energy density (in excess of 300 kWh/m<sup>3</sup> ) thermal storage system, that can store heat at temperature around 1000°C [14, 15]. The unique aspects of this system are the selection of an alkali halide salt with high melting temperature and a corrosion resistant cheap ceramic container material. The thermal storage unit will be coupled with a high solar concentrator system (1000–10,000×). As a part of an on-going project at RKDF University in near vicinity of RGPV, funded by MNRE, the project collaborator in Solar thermal, the Rensselaer Polytechnic Institute of USA has developed flux grown crystals of high melting temperature (700–1500°C) mixed alkali halide compounds doped with metallic impurities to enhance thermal conductivity. The trade-off between material density, specific heat capacity, thermal conductivity and cost of raw material has been evaluated to develop a material system that could meet the system's specification at cost of energy storage lower than current electrochemical systems (batteries). In addition, a SiC based composite polymeric coating solution has been developed to avoid corrosion of steel containers used for the thermal storage unit [16]. These materials have been shipped to RKDF University and incorporated into the field unit (test-bed). The test-bed at RKDF comprises of a thermal storage unit, Fresnel lens based solar tracking unit to focus sunlight into the thermal storage media and a steam generation unit (for future electricity generation using a steam turbine). **Figure 5** shows the installation and initial evaluation activities of the solar thermal storage unit at RKDF University.

The expected physical outcomes of the project of CSP integration with CCS as discussed above are in terms of establishment of the pilot plant of CO2 capture and sequestration on an actual thermal power station for future development of technology of CCS in India and countries between tropic of cancer & capricorn bestowed with high solar DNI [1, 7].

Test results have shown that the innovative halide salt used as thermal storage material stores heat to such an extent that it retains heat for over 5 days to be able to produce steam (**Figure 6**). This innovative halide salt was also tested in the pilot plant shown at **Figure 5**. The biggest challenge in this project is, however, the development of Alkali Halide Salt indigenously for which efforts are under way at RKDF University to procure some of the key components for growing crystals with high energy density, capable of retaining heat. Also efforts are underway towards indigenous development of Heliostats, Fresnel lens and low cost trackers.

**Figure 5.** Solar thermal storage unit at RKDF University.

potential pathway for small (local) and large (utility power plants) scale applications. Thermal storage systems provide a unique opportunity to store energy locally in the form of heat that cannot be transported over long distances. Current thermal storage systems are still in its infancy. The most common ones are large, water-heating storage tanks and molten salt-based systems at solar power plants. These systems have been designed based on the economics of water and salt, the heat capacity of water, and the latent heat of salts. Research on a large host of sensible heat storage and phase-change materials have been conducted over the past two decades. The materials parameters that are relevant for this application are: melting point, boiling point, vapor pressure, density, heat capacity, thermal conductivity, latent heat of fusion and chemical reactivity. While it is intuitive that increasing the temperature of storage could pack in more energy, barriers to the development and deployment of high energy density storage remain, including handling materials at high temperatures, associated systems costs, and operating costs. Thus sensible thermal storage systems are cost prohibitive. Phase change materials (PCM) do provide a viable economical solution for higher energy storage density. However, operation temperatures limit current PCM systems; higher temperatures cause chemical instability and reactivity with containers. Development of affordable high-density thermal storage system will only be possible by utilizing low cost earth abundant thermal storage materials in conjunction with suitable thermally insulating container materials. Current heat storage systems utilize either sensible heat storage (i.e. water in storage tanks) or latent heat storage (i.e. phase-change materials such as molten salts). The relatively low operating temperatures of these systems limit their capacity to store thermal energy; storage systems with higher

The technologies which hold promise for achieving temperatures in the range of 150–600°C and beyond can be categorized by the phases of matter of the materials used: liquid, gaseous,

• A liquid pathway is considered to look much like today's molten salt two tank tower con-

• Gaseous pathways use an inert gas flowing through a receiver to absorb the solar energy and then transfer the thermal energy to a storage system and/or the turbine working fluid. • Solid pathways involve solid inert media which absorbs solar radiation and stores that energy as heat. When electric power is needed, the turbine working fluid is heated by the

In this CCS integrated with CSP project we examined several options of 'Solid Pathway' such as cast iron core of Mount Abu 1 MW solar plant used for steam generation, CL-CSP plant at the State technological University of MP, RGPV, in Central India in which pebbles/rock storage has been proposed for energy storage for heating air in primary cycle and steam in

In this CSP to CCS integration project, we are developing an affordable high energy density

) thermal storage system, that can store heat at temperature around

figuration, but using a suitable high temperature and cost effective HTF/TES.

temperatures would be more economical.

102 Carbon Capture, Utilization and Sequestration

solid, as under:

solid media.

secondary cycle.

(in excess of 300 kWh/m<sup>3</sup>

addition, the path to zero-emissions must be progressive and in line with the progress of new and renewable technologies of hydro, solar and wind. The first step towards in this progres-

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105

Indigenous development of critical components of solar thermal plants for integration with CCS is nevertheless important. The following is a list of identified components that will be necessary to be developed within India at ultra-low cost by technology licensing and manufacturing technology transfer approaches by commercial entities (from abroad) to translate

**1.** Large area high optical quality Fresnel lens/Heliostats/Fresnel Reflectors manufacturing

**2.** High thermal storage density material development for 24 × 7 heat storage.

\* and Partha S. Dutta<sup>2</sup>

2 Smart Lighting Engineering Research Centre RPI, NY, USA

Indian context. Energy Procedia. 2017;**114**:1288-1296

plants in India. Energy Procedia. 2014;**54**:431-438

\*Address all correspondence to: vksethi1949@gmail.com

**5.** Energy efficient, low maintenance cost thermal transport systems for heat exchange.

[1] Sethi VK, Vyas S. An innovative approach for carbon capture & sequestration on a thermal power plant through conversion to multi-purpose fuels—A feasibility study in

[2] Rao Anand B, Piyush K. Cost implication of carbon capture and storage for coal power

[3] Yang A, Cui Y. Global coal risk assessment–data analysis and market research—A working paper. World Resources Institute. 2012. http://www.wri.org/publication/global-

[4] Monthly All India Generation capacity Report. India: Central Electricity Authority, CEA; 2013. Available from: http://www.cea.nic.in/reports/monthly/executive\_rep/dec13.pdf

sive path should be CCS.

with low cost.

**Author details**

Vinod Krishna Sethi<sup>1</sup>

**References**

the existing technology for large scale adoption:

**3.** Corrosion resistance nano-coating process.

**4.** Ultra-low cost solar trackers.

1 RKDF University, Bhopal, India

coal-risk-assessment

**Figure 6.** Thermal cooling profile testing of the halide salt at RPI, USA.
