National Energy Efficiency Conference 2015 Date: 6 - 7 October 2015

Venue: MAX Atria @ EXPO Singapore

Session: Breakout Track 4B (7 October, 1445 – 1545 hrs)

Title of Session: Emerging technologies

Speaker: Dr Alessandro Romagnoli (Assistant Professor, NTU)

Presentation Title:

Waste heat recovery in industrial processes via thermal energy storage

Notes:

Major energy inefficiency in thermal systems, particularly large ones, is the generation of waste heat and the lack of utilisation of this waste heat. About 20 – 50% of industrial energy consumption is ultimately discharged as waste heat.

The extraction potential for surplus waste heat from industrial processes represents a significant resource that is only partially exploited to date.

Waste heat from flue gas of energy intensive industries (e.g. steel industry, foundries, refinery) has highly unsteady thermal power profile as a result of the variation in thermodynamic parameters (e.g., temperature and mass flow rate) over time.

The current waste heat recovery (WHR) technologies (e.g. Organic Rankine Cycle (ORC) system) are designed to operate at the maximum thermal power point. But they are mainly operated in off-design point (low efficiency working zone).

Using a phase change material (PCM) device, the off-design operating point can be shifted closer to the design point, thereby increasing the efficiency of the WHR systems.

A case study was done on a steel manufacturer o In existing system, flue gas (> 800°C) from billet furnace is used to preheat the air

entering the furnace. The resulting flue gas (~400°C) then enters the waste heat boiler of the ORC system to generate electricity.

o In proposed system, the PCM device was installed between the furnace and air-preheater. The PCM device operates in two modes: charging mode (PCM is melting) and discharging mode (PCM is solidifying). Part of the flue gas enters the PCM device to charge the PCM material. Ambient air is also introduced into the PCM device to store thermal energy. The heated ambient air leaving the PCM device is mixed with the flue gas entering the waste heat boiler to increase the thermal power of the flue gas.

o With the PCM device, the efficiency of the WHR system was increased by 33%.

The payback period of the PCM device is about 3 to 4 years. Key Findings:

There is still significant opportunity to improve energy efficiency in industrial processes through WHR.

The performance of WHR systems is largely affected by the variability of thermal power from flue gas

The new PCM thermal storage device, which modulates the thermal load variability, has been assessed based on real experimental data collected from an electric arc furnace.

Installing the PCM thermal storage device with the ORC showed that it is possible to improve recovery of waste heat by more than 30%

Current research activity will focus on pilot scale testing, optimization of the heat exchange process and corrosion effects

Key Recommendations:

National Energy Efficiency Conference 2015 Date: 6 - 7 October 2015

Venue: MAX Atria @ EXPO Singapore

Speaker: Prof Hellwig Runa Tabea (Associate Professor/Cluster Director, Solar Energy Research Institute of Singapore (SERIS), NUS) Co-authors: Dr M Arifeen Wahed (Head, Solar Thermal Systems group, SERIS, NUS) Monika Bieri (Research Associate, SERIS. NUS)

Presentation Title:

Solar thermal applications for industrial process heat in the tropics: Prospects and challenges

Notes:

About 30% of industry energy consumption is used for process heat applications

Singapore has high potential for solar as it enjoys a relatively high annual irradiation of 1630 kWh/(m2.a), high daily availability and little monthly variation.

While solar photovoltaics generate electricity, solar thermal collectors generate thermal energy for heating, cooling and electricity generation.

Solar thermal systems for process heat application can be designed with or without storage systems, and could be closed or open cycle.

Solar thermal for process heat application primarily consists of two loops: (a) a collector loop to harvest solar energy, , and (b) a process heat loop where the heat is discharged from the working fluid to the process fluid. A heat storage loop could be introduced into the system if necessary.

Collector efficiency depends on the following factors:- o Collector type; o Collector brand; o Tilt angle & orientation; o Targeted temperature level; and o Inlet temperature.

SERIS is currently testing different collectors in its outdoor solar thermal collector testing facility. Based on the results obtained, the thermal collector efficiency ranges from 50 – 80% depending on the design and settings.

A sensitivity analysis using the levelised cost of energy (i.e., ratio of total life cycle cost to total lifetime energy production) shows that solar thermal systems are cheaper than gas-fuelled heating systems. The best value for solar thermal systems is 11 cents/kWhth in comparison to 21 cents/kWhth for gas-fuelled heating systems. The results are dependent on the future energy price assumed.

Low adoption of solar thermal could be due to the high upfront investment cost.

Factors to consider when implementing solar thermal systems:- o Detailed analyses of processes o Decrease possible energy waste cases o Determine demand for process heat through measurements o Determine cost of current process including consumption, maintenance and other

lifecycle cost o Selection of collector and necessity of heat storage o Determine potential solar heat contribution to cover the demand o Consider use of renewables (e.g. solar thermal) when major replacements are

planned

Factors to consider in solar thermal system installation:- o Solar collector design including shading analysis, right choice of collector for

application o Hydraulic design including piping and pumps o Water storage unit

National Energy Efficiency Conference 2015 Date: 6 - 7 October 2015

Venue: MAX Atria @ EXPO Singapore

o Proper insulation o Efficient control system

Solar thermal systems are installed at the canopy of South Beach Development by Foster & Partners. They can also be installed on roofs of walkways to provide shade.

Key Findings:

Solar thermal systems are applicable to process heating in industrial facilities. Key Recommendations:

Moderator: Dr Christopher Yap (NUS)

Issues Raised: Q: When will PCM device be commercially available? A: The device is currently undergoing control testing in Italy. The pilot test will only start next year in Sweden. Q: What is holding back industries from adopting waste heat recovery technologies? A: The major concerns are: (i) process disruption due to the installation of WHR systems, and (ii) low efficiency of existing WHR systems. With new technologies such as solid state technology and renewables, there will be more opportunities for WHR. Q: Is it better to go for solar photovoltaics (PV) or solar thermal system? A: it depends on the process, whether the process requires electricity or heat. Each system has its own advantages and disadvantages and there is no competition between both systems. Q: What is the opportunity of a combined solar PV and solar thermal system? A: Solar thermal systems can used to cool down solar PV systems. Such combined systems are less applicable to process heating applications. Q: What is the temperature range for current solar thermal systems? A: Up to 150°C. For higher temperatures, concentrator collectors could be used. However, such collectors are not feasible in Singapore as Singapore receives more diffused radiation than direct radiation. Q: Are there any applications of solar PV in vertical walls? A: Building integrated PV can be mounted on vertical walls. They have the same efficiency as when mounted on rooftops. However, the potential is much lower due to the higher angle of solar irradiation. Summary:

Rapporteur(s): Yeo Wee Kay (NEA), Eunice Koh (NEA)