It is proposed to install 2 prototypes of Waste heat recovery unit (WHRU) to generate power from the gas coming out of the Yankee cylinder chimney of the tissue dryer (machine #6).

Initial design decisions

Data to be considered in the design of the unit:

  • Type of flue gases: Hot air
  • Gas velocity: approximately 10 m/s.
  • Relative humidity:
  • Gas temperature: 200 ºC –240 ºC.
  • Water temperature: 14 ºC -25 ºC.
  • Diameter of the chimney: 900 mm

The two WHRU modules will be installed on a flanged decagonal spool at the end of the chimney.

The decagonal tube will consist of a section of pipe or similar that is equipped with a flange in each end. The decagonal tube will be prepared to integrate ten WHRU modules. This decagonal tube will be installed on the existing exhaust fume chimney.


The exhaust fume chimney has an outside diameter of 900 mm with a thickness of 3 mm.

The outlet temperature of the exhaust fumes from the burners has an average of 200 ºC (with peaks of 210 ºC), according to the measurements provided by Gomà-Camps.

For the WHRU cooling, water coming from the cooling towers of the installation at 14-20 ºC may be available.


  • WHRU modules will be equipped with waterblocks for the system cooling with water.
  • The cooling water system will be provided with air bleed valves to avoid the presence of air in the water circuit.
  • For monitoring the correct functioning of the prototype, 2 types of sensor nodes will be installed:
    – Type 1-Temperature Node: Th, Tc and Tgases output.
    – Type 2-Node Wattmeter to measure the power generated by the system. Said node will be installed inside the electrical panel.
  • The technology to be applied in the communication between the sensor nodes and the Gateway will be LoRa.
  • A Gateway will be installed to collect all the data sent by the sensors.
  • The Gateway will be powered from the power grid.
  • The communication between the Gateway and the server will be via 3G/4G.
  • DAEVIS platform will be displayed for data visualization.
  • An electrical cabinet equipped with electrical protections and an inverter will be installed to transform DC to AC to inject the power generated by the WHRU modules into the power grid.
  • Said electrical cabinet will be powered from the power grid.
  • Plumbing work to get the cooling water to the WHRU modules from the cooling tower will be carried out by Gomà-Camps maintenance personnel.
  • The electrical connection work (placement of the electrical cabinet, cable routing and electrical connections with the cabinet, …) will be carried out by Gomà-Camps maintenance personnel.
  • Mechanical cutting and welding work will be carried out by a mechanical assembly company hired by Gomà-Camps.
  • Because of the floor is non-practicable and the exhaust fume chimney is 12 m high, a vertical lift and a crane truck will be required to carry out the installation works.


Specific points

A Heat R-System energy recovery system will be installed in a configuration of 2 WHRU modules with 6 40×40 thermoelectric generators, which incorporates Cold Plate technology for the cooling of the modules located in the chimney of the tissue dryer.
The sensors node will be installed inside an independent box that will be installed close to the 2 WHRU modules.

The distribution of the water to the waterblocks will be done by means of a T-fitting with silicone hoses.   The cooling system will be equipped with air bleed valves and anti-return connectors to prevent the presence of air. 

WHRU modules will penetrate the conduit with anodized aluminum heatsinks.

Mechanical design

The installation of a decagonal tube is chosen to fix two WHRU modules and the sensors node into the 900 mm diameter chimney.

As for WHRUs units, the installation of six 40×40 thermoelectric generators in each module is chosen. These thermoelectric generators have a non-continuous working limit of 250ºC and a continuous limit of 200ºC. As long as there is no water cut, these cells will work at an optimal working point. In the event of a water cut, the system may fail.

The WHRU module is mainly made up of the following components:

1. 240x40x63 mm aluminum sensor. Black anodized finish to improve corrosion resistance.
2. Frame-Cell Support-Mica Insulator. This component will act as a fixation to the mounting conduit, and at the same time will act as an insulator, since this material has 0.3 W / mK of thermal conductivity and will improve the performance of the equipment. In addition, it will serve to house the cells.
3. Cold Plate. Open liquid cooling system (water) that will be in charge of exerting pressure force on the cells, in addition to cooling the cold side of the cells in order to obtain the maximum thermal differential.
4. Powerbox support. Made of carbon steel. It will act as a support for the power box and will be located on the Cold Plate in order to prevent it from heating up.
5. Powerbox. the PCB will be located inside the box.
6. Thermoelectric generator. Each WHRU module will be equipped with 6 thermoelectric generators with dimensions 40x40x3.6 mm, which can produce up to 6.9 W.

In order for the system to work properly, it is very important that the cooling system meets the following characteristics:

– Fluid: clean water
– Flow: 2 to 5 l / min
– Pressure: 1-2 bars
-Temperature: 10 – 30 ºC

Electrical design

We will place an electrical cabinet with its respective electrical safety: two 16A fuses at the input of the inverter, a 10A magnetothermic switch that cuts the phase and the neutral.

A network synchronized inverter is required, which goes from the 14V output of the system to 230V / 50Hz of the network. There is also a wattmeter to be able to read the power generated remotely.

A 5V power supply is installed for the operation of the sensor nodes and the wattmeter reader, and another 12V source to supply the sensor if the distance between the cabinet and the modules requires it.


Electronics design

It is required to transform the input voltage from the thermoelectric generator into the required voltage of 14V. This will be done by a set of several CC/CC Boost converters. The control of the CC/CC boost converters operation will be performed by a control printed circuit board.

With an estimated temperature on the hot side of around 150ºC and 25ºC on the cold side, the input resistance of the converter should not exceed 6.7Ω, so the power management system should be made not to exceed a certain value that will be adjusted with tests.

The electronic boards will be located inside power boxes.

Regarding sensorization, two nodes will be installed to monitor the proper operation of the WHRU modules: the first with 4 temperature points (hot face, cold face, gas inlet, gas outlet) and a second one to read the Wattmeter data at the system output.



Communication platform

The IoT communication nodes will receive temperature and the generated power data from the sensors. These data will be sent using LoRa communications to the gateway. The restriction of using this type of communication is that it does not allow obtaining data in real-time. Each sample will be sent a certain time. The order of magnitude of time that we must take into account is minutes.
The data will be sent to a Gateway, which will treat it appropriately.


  • There are distance limitations in terms of communications and therefore LoRa technology will be used for the communication of the nodes
  • A RAK7249 gateway will be mounted. The gateway packet forwarder is configured to send the data from the things network server to the AEInnova account for node management and the gateway itself.
  • A packet forwarder is deployed that acts as a gateway between the MQTT server of The things network and the DAEVIS instance for the Goma Camps client.
  • For communications from the gateway to the server, the 3G / 4G communications module that incorporates the gateway will be used. To do this, a mobile phone SIM with data must be used to send data to the LoRa server.
  • DAEVIS platform will be used for data explotation.