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LIFE - HEAT-R

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Celsa: Conclusions

The waste heat recovery technology has been tested by these five different prototypes with different variations in power electronics, thermal collector contact surfaces, cooling system and the thermoelectric generators to configure the best option for each type of heat source.

Efficiency is one of the main parameters analysed in each project. This parameter shows how much energy is extracted from waste heat.

The efficiency of the prototype depends on the heat source, the heat collector type and the cooling system applied.

CELSA group produces 2.4 million tons of steel per year. Production is separated into corrugated and smooth round rods, rolled wire, flats rods, squares, angles rods, and structural sections.

The energy recovery system (Heat R-System) installed in the industrial plant that CELSA has in Castellbisbal (Barcelona) makes use of the waste heat generated by radiation in the beam blank cooling area.

The operating cycle of the beam blank production is 24 hours a day, 7 days a week, and the temperature of the heat source is about 600 ºC although the temperature in the metal heat collection plate is about 240 ºC.

The recovery system obtains heat by conduction through the contact between the heat collector of the WHRU and the metal heat collection plate that receives the radiation from the beam blanks. Therefore, the recovery system is non-intrusive.

WHRU modules uses water heat-exchanger (water-block) for their cooling to obtain the maximum temperature difference between the two sides of the Peltier cells. Water is pumped from an internal cooling water line. The water-cooling temperature is about 25 ºC.

In this project, the energy recovery system is based on this type of WHRU:

 

WHRU – WBCD100

 

 

 

  • Cooling system principle: Forced water convention
  • Cooling components Cold plate or water heat exchanger (waterblock).
  • Heat capture system principle Forced air convection – gas exhaust.
  • Thermal collector Plane thermal collector
  • Electrical energy generator Thermoelectric generator TEG – Peltier cell
  • Peltier cell number 36 cells 40 *40 mm

 

The main feature of this device is that it groups a set of 36 thermoelectric generators into a single unit. This design was created to group as many thermoelectric generators as possible in the smallest possible space, optimising the ratio of power generated per unit area.

 

Results

 

Thermal collector plate temperature 200 – 248 ºC
Generation area WHRU 1705,7 cm2
Mean power generated *32 W
Maximum power generated *40 W
Energy generated *280,32 kWh/year
Power density. *47,62 W/m2
Heat dissipated by the heat source 685 W
Heat flow through Heat R-System by conduction *1126 W
Efficiency *3,55 %

 

To generate more energy, it is necessary to capture the maximum amount of heat flow. This is possible if the system is intrusive and there is contact between the fins of the heat collector and the hot gases. This is not the case in this project.

 

In CELSA, the system is non-intrusive and the heat is obtained by surface contact between the heat collector and the metal heat collection plate, which receives the heat by radiation and therefore, increases its temperature. However, when the WHRU is in contact with the metal heat collection plate the surface temperature of the heat collector is reduced and, consequently, the efficiency is reduced.

 

On the other hand, there is a higher heat transfer due to the higher number of mounted Peltier cells.

 

The action of the forced water cooling system allows a significant temperature differential between the two sides of the Peltier cells, which results in higher electrical power generation, but the efficiency is not as high as if the system were intrusive.

 

From the standpoint of the installation, the water-cooling system requires a hydraulic loop with a pump. It is essential to ensure a continuous supply of cooling water to avoid damaging the prototype by exceeding the maximum working temperatures of the components. Therefore, installing two pumps instead of one or automating the start-up of the pump when the process starts are options to ensure the water supply. It is also crucial to ensure that all valves are open in the hydraulic circuit.

 

On the other hand, the quality of the water supply is important. The water must be free of suspended solids to avoid possible clogging that could hinder or prevent the water supply and thus damage the equipment.

 

Ciments Molins: Conclusions

The waste heat recovery technology has been tested by these five different prototypes with different variations in power electronics, thermal collector contact surfaces, cooling system and the thermoelectric generators to configure the best option for each type of heat source.

Efficiency is one of the main parameters analysed in each project. This parameter shows how much energy is extracted from waste heat.

The efficiency of the prototype depends on the heat source, the heat collector type and the cooling system applied.

The activity of Ciments Molins Group focuses on manufacturing, distributing and selling cement, concrete, mortars, aggregates and concrete prefabricates, and running activities and production plants in different countries.

The energy recovery system (Heat R-System) installed in the industrial plant that Ciments Molins has in St. Vicenç dels Horts (Barcelona) makes use of the waste heat generated in the walls of the rotatory kiln used for firing the clinker and which are close to the burner.

The operating cycle of the rotatory kiln is 24 hours a day, 7 days a week, and the heat source temperature is about 200 ºC although the temperature inside the rotatory kiln is up to 1000ºC. The device must withstand ambient temperatures up to 40 ºC.

The recovery system obtains heat by conduction and is non-intrusive.

The forced air generated by fans cools the equipment to obtain the maximum temperature difference between the two sides of the Peltier cells.

In this project, the energy recovery system is based on a new type of WHRU:

 

WHRU – HSCD100

 

 

  • Cooling system principle: Forced air convention
  • Cooling components Heat sink with four fans.
  • Heat capture system principle Conduction
  • Thermal collector Plane thermal collector.
  • Electrical energy generator Thermoelectric generator TEG – Peltier cell
  • Peltier cell number 36 cells 40 *40 mm

 

The main feature of this device is that it groups a set of 36 thermoelectric generators into a single unit. This design was created to group as many thermoelectric generators as possible in the smallest possible space, optimising the ratio of power generated per unit area.

 

Results

 

Heat source temperature 191 – 213 ºC
Generation area WHRU 1705.7 cm2
Mean power generated 5.43 W
Maximum power generated 6.86 W
Energy generated 47.6 kWh/year
Power density 31.83 W/m2
Heat dissipated by the square heat source 310 W
Heat flow through Heat R-System by conduction 491 W
Efficiency 1.40 %

 

Prototypes based on a forced air-cooling system with a heat collector in contact with a hot surface have been found to be the least effective and efficient.

To generate more energy, it is necessary to capture the maximum amount of heat flow. This is possible if the system is intrusive and there is contact between the fins of the heat collector and the hot gases. At Ciments Molins, the system is non-intrusive and the heat is obtained by surface contact between the heat collector and the hot wall of the rotary kiln.

On the other hand, there is a higher heat transfer due to the higher number of Peltier cells mounted.

Unlike the forced water-cooling system, the forced air-cooling system cannot absorb all the heat. This means that there is no temperature difference between the sides of the Peltier cells and the efficiency is lower.

Distiller Chemical Industry: Conclusions

The waste heat recovery technology has been tested by these five different prototypes with different variations in power electronics, thermal collector contact surfaces, cooling system and the thermoelectric generators to configure the best option for each type of heat source.

Efficiency is one of the main parameters analysed in each project. This parameter shows how much energy is extracted from waste heat.

The efficiency of the prototype depends on the heat source, the heat collector type and the cooling system applied.

DISTILLER treats and manages industrial waste using distillation processes to recover solvents and treat contaminated aqueous solutions.

Thermal oil is used to supply the necessary heat to perform the distillation processes. Thus, the factory has thermal oil boilers to heat and recirculate the oil to different energy consumers through a close circuit.

The energy recovery system (Heat R-System) installed in industrial waste manage plant that Distiller has in Sta. Perpetua de la Mogoda (Barcelona) makes use of the waste heat generated in a WOGA thermal oil boiler.

The operating cycle of the dryer is 24 hours a day, 7 days a week, and the gas temperature varies from 130 to 220 ºC. The device must withstand ambient temperatures up to 40 ºC and sun exposure.

The recovery system that is installed is intrusive: the fins of the WHRU thermal collectors are installed inside the chimney to capture the maximum amount of heat from the gases. Although intrusive, this system does not affect the operation of the boiler, as it does not cause any pressure drop or condensation.

WHRU modules uses water heat-exchanger (water-block) for their cooling to obtain the maximum temperature difference between the two sides of the Peltier cells. The water is pumped from a well. The water-cooling temperature is 25 ºC.

In this project, the energy recovery system is based on a new type of WHRU:

 

WHRU -WBCV200

 

 

 

  • Cooling system principle: Forced water convention
  • Cooling components Cold plate or water heat exchanger (waterblock).
  • Heat capture system principle Forced air convection – gas exhaust.
  • Thermal collector Intrusive convectional heat sink
  • Electrical energy generator Thermoelectric generator TEG – Peltier cell
  • Peltier cell number 36 cells 40 *40 mm

 

The main feature of this device is that it groups a set of 36 thermoelectric generators into a single unit. This design was created to group as many thermoelectric generators as possible in the smallest possible space, optimising the ratio of power generated per unit area.

 

 

Results

 

Exhaust gas temperature 130 – 220 ºC
Generation area of two WHRU. 1705.7 cm2.
Mean power generated *54.72 W
Maximum power generated *96.50 W
Energy generated *479.30 kWh/year
Power density *565,80 W/m2
Heat flow in the exhaust gas
Heat flow through Heat R- System *2275 W
Efficiency 4.24 %

 

 

This device shares many similarities with the Goma Camps prototype in terms of heat collection and cooling system, except that Distiller’s WHRU device packs more Peltier cells into a smaller area. In other words, Distiller’s WHRU device is equivalent to six Goma Camps devices.

The prototype developed for the Distiller’s project has the highest efficiency with a theoretical efficiency of around 4.24 %.

In this way, forced water cooling system together with forced convective flow heat collection based on the installation of the heat collector in contact with the hot gases is the best configuration for achieving the best performance of the prototypes.

This type of thermal collection uses a forced convective flow, which increases the temperature of the Peltier cells.

In addition, the power density of this WHRU device is increased by grouping 36 Peltier cells in a smaller area.

On the other hand, the action of the forced-water cooling system results in a significant temperature differential between the two sides of the Peltier cells which translates into a higher electrical power generation.

-From the standpoint of the installation, the water-cooling system requires a hydraulic loop with a pump. It is essential to ensure a continuous supply of cooling water to avoid damaging the prototype by exceeding the maximum working temperatures of the components. Therefore, installing two pumps instead of one or automating the start-up of the pump when the process starts are options to ensure the water supply. It is also crucial to ensure that all valves are open in the hydraulic circuit.

 

On the other hand, the quality of the water supply is important. The water must be free of suspended solids to avoid possible clogging that could hinder or prevent the water supply and thus damage the equipment.

Gomà Camps Paper Industry: Conclusions

The waste heat recovery technology has been tested by these five different prototypes with different variations in power electronics, thermal collector contact surfaces, cooling system and the thermoelectric generators to configure the best option for each type of heat source.  

Efficiency is one of the main parameters analysed in each project. This parameter shows how much energy is extracted from waste heat.  

The efficiency of the prototype depends on the heat source, the heat collector type and the cooling system applied. 

In the paper industry tissue paper dryers are well known. They are equipped with a hood that blows hot air at high speed against the tissue paper and a rotating drying cylinder called Yankee that is partially covered by the hood. The tissue paper is dried by combining the drying cylinder that transfers heat by contact from the superheated steam circulating inside and the hood that dries by heat and mass transfer. 

The energy recovery system (Heat R-System) installed in the tissue paper manufacturing plant that Gomà-Camps has in La Riba (Tarragona) makes use of the waste heat generated in a tissue paper dryer.  

The operating cycle of the dryer is 24 hours a day, 7 days a week, and the gas temperature varies from 200 to 240 ºC. The device must withstand ambient temperatures up to 40 ºC and sun exposure. 

The recovery system that is installed is intrusive: the fins of the WHRU thermal collectors are installed inside the chimney to capture the maximum amount of heat from the gases. Although intrusive, this system does not affect the operation of the dryer, as it does not cause any pressure drop or condensation. 

WHRU modules uses water heat-exchanger (water-block) for their cooling to obtain the maximum temperature difference between the two sides of the Peltier cells. The water is pumped from a tank. The pump used to pump the cooling water to the water blocks works so long as the Yankee dryer does. The water-cooling temperature is 14-20 ºC.  

In this project, the energy recovery system is based on a new type of WHRU: 

 

WHRU -WBCV100

 

 

  • Cooling system principle: Forced water convention  
  •  Cooling components Cold plate or water heat exchanger (waterblock).  
  • Heat capture system principle Forced air convection – gas exhaust.  
  • Thermal collector Intrusive convectional heat sink  
  • Electrical energy generator Thermoelectric generator TEG – Peltier cell 
  • Peltier cell number 6 cells 40 *40 mm 

 

 

Gas temperature 200-240 ºC
Generation area two WHRU 531 cm2
Mean power generated 17.5 W
Maximum power generated 25.92 W
Energy generated 153.30 kWh/year
Power density 329.40 W/m2
Heat flow in the exhaust gas 2.31 MW
Heat flow through Heat R-System 813.20 W
Efficiency 3.19 %

 

 

Results

 

In terms of power generation, this device produces more electrical energy per surface area than the prototype installed at Bodegas Torres. Consequently, its efficiency is higher. However, unlike a solar panel that has a system efficiency of approximately 20 %, the heat recovery system installed in Goma-Camps has a system efficiency of approximately 3%.  

 

– To generate more energy, it is necessary to capture the maximum amount of heat flow. Therefore, the contact surface between the heat collectors and the hot gases should be as large as possible. Therefore, the installation of the fins in contact with the gas increases the energy generation. However, the length of the fins is limited because a longer length could lead to a pressure drop in the gas flow which could cause emission problems in the installation. 

 

-From the standpoint of the installation, the water-cooling system requires a hydraulic loop with a pump. It is essential to ensure a continuous supply of cooling water to avoid damaging the prototype by exceeding the maximum working temperatures of the components. Therefore, installing two pumps instead of one or automating the start-up of the pump when the process starts are options to ensure the water supply. 

 

On the other hand, the quality of the water supply is important. The water must be free of suspended solids to avoid possible clogging that could hinder or prevent the water supply and thus damage the equipment. Therefore, Goma-Camps linked the pump operation to the dryer. In this way, the water pump works while the dryer is working. 

  

-The Yankee cylinder is used in all paper manufacturing factory. Therefore, Goma – Camps is completely scalable to install waste heat recovery systems in other paper manufacturing companies. 

Família Torres winery industry: Conclusions

The waste heat recovery technology has been tested by these five different prototypes with different variations in power electronics, thermal collector contact surfaces, cooling system and the thermoelectric generators to configure the best option for each type of heat source.

Efficiency is one of the main parameters analysed in each project. This parameter shows how much energy is extracted from waste heat.

The efficiency of the prototype depends on the heat source, the heat collector type and the cooling system applied.

The energy recovery system (Heat R-System) installed in Waltraud winery that Bodegas Torres has in Pacs del Penedès makes use of the waste heat generated in the biomass boiler located in the Waltraud winery.

The operating cycle of the biomass boiler is 24 hours a day, 7 days a week, and the gas temperature varies from 150 to 300 ºC depending on the fuel used, which can be stumps and/or forest mass. The ambient temperature ranges between 35 and 45 ºC, and there is no cooling water in the installation.

The recovery system that is installed is intrusive: the fins of the WHRU thermal collectors are installed inside the chimney to capture the maximum amount of heat from the gases. Although intrusive, this system does not affect the operation of the boiler, as it does not cause any pressure drop or condensation.

The forced air generated by fans cools the equipment to obtain the maximum temperature difference between the two sides of the Peltier cells.

In this project, the energy recovery system is based on two types of WHRU:

 

WHRU-HPCV100

 

 

  • Cooling system principle: Controlled forced air convention.
  • Cooling components: Heat sink composed of a heat pipe, flat fins, and one fan with variable speed through the PWM control system to maximize the temperature difference between Peltier cell sides.
  • Heat capture system principle: Forced air convection – gas exhaust.
  • Electrical energy generator: Thermoelectric generator TEG – Peltier Cell.
  • Peltier cell number: 4 cells 40*40 mm.

 

WHRU-HPCV50

 

 

  • Cooling system principle: Controlled forced air convection.
  • Cooling components: Heat sink composed of a heat pipe, flat fins, and two fans with variable speed through PWM control system to maximize the temperature difference between Peltier cells sides.
  • Heat capture system principle: Forced air convection – gas exhaust.

 

Gas temperature 150 – 300 ºC
Generation area 843.30 cm2
Mean generated power 8.63 W
Maximum generated power 14 W
Generated energy 75.56 kWh/year
Power density 102.33 W/m2
Heat flow in the exhaust gas 80.50 kW
Heat flow through Heat R-System 722.22 W
Efficiency 1.94 %

 

Results

 

– In contrast to a 280 W solar panel with an efficiency of 17 % and a surface area of 1.63 m2, which represents a power density of about 171 W/m2, the power density obtained with this prototype is about 102 W/m2 with a system efficiency of 1.94 %. Therefore, despite its low efficiency, the heat recovery device is close to the values generated by solar energy using the same surface area.

 

– The prototype consists of installing two different types of heat recovery units to compare their performance. When analysing the results, the larger the heat sink, the better the performance of the WHRU.

 

– In addition, in order to generate more energy, it is necessary to capture the maximum amount of heat flow. Therefore, the contact surface between the heat collectors and the hot gases should be as large as possible. Therefore, the installation of the fins in contact with the gas increases the energy generation. However, the length of the fins is limited because a longer length could lead to a pressure drop in the gas flow which could cause emission problems in the installation.

 

– Prototypes based on a forced air cooling system have proven to be less effective and efficient than others based on a water cooling system.  In addition, a fan has a life cycle of approximately 5 years in regular operation. After this time, the fans need to be replaced. In addition, the fan blades become dirty when the prototype is installed in a polluted industrial environment. This causes a decrease in the performance of the prototype.

 

Celsa Steel Industry: Pilot Installation

The installation was carried out on December 17, 2021.

The installation of the pilot required electrical and plumbing works that were carried out prior to the installation of the pilot by the maintenance staff of Celsa, following the instructions of the mechanical and the electronic department of AEInnova.

The final installation of the recovery system was carried out by Celsa’s staff following the instructions of AEInnova’s staff.

Below you can see some of the photographs taken at the installation.

 

 

Ciments Molins: Pilot Installation

The installation was carried out on May 31, 2021 and on September 28, 2021.

The final installation of the recovery system was performed jointly with the staff of AEInnova and Ciments Molins.

Below you can see some of the photographs taken at the installation.

 

Distiller Chemical Industry: Pilot Installation

The installation was carried out on December 24, 2020.

The installation of the pilot required mechanical works that were performed by a specialized company following the instructions of the mechanical department of AEInnova.

The final installation of the recovery system was performed jointly with the staff of AEInnova and Distiller.

Below you can see some of the photographs taken at the installation.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Celsa Steel Industry: Prototype Implementation

All components of the heat recovery system are integrated and connected to generate the maximum amount of power from the waste heat source.

In CELSA, a metal support is required to fix the plate that captures heat by radiation as well as the heat recovery unit (WHRU).

 

Figure . Support and metal plate

Ciments Molins Cement Industry: Prototype Implementation

All components of the heat recovery system are integrated and connected to generate the maximum amount of power from the waste heat source.

The heat recovery system requires a cooling system for proper operation and to avoid thermal collapse of the system. Thus, in Ciments Molins the prototype uses four fans to generate forced air.

 

Figure. Fan

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