# D4.3 Report on the Control System Design

Frédéric Pithoud, Julian Roschen, Richard Aumann

► To cite this version:

Frédéric Pithoud, Julian Roschen, Richard Aumann. D4.3 Report on the Control System Design. [Research Report] European Union. 2022. hal-04750966

HAL Id: hal-04750966

https://cnrs.hal.science/hal-04750966v1

Submitted on 28 Oct 2024

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
<figure><img src="image_2.png" /></figure>

<figure><img src="image_3.png" /></figure>

POLYPHEM

THE FUTURE OF SMALL-SCALE CSP PLANTS

# POLYPHEM
## Small-Scale Solar Thermal Combined Cycle

### D4.3 Report on the control system design

**Date of delivery** 01/09/2022

**Author(s)** Frédéric Pithoud, Julian Roschen, Richard Aumann

**Organisation** CNRS-PROMES, KAEFER, ORCAN

<figure><img src="image_4.png" /></figure>

<figure><img src="image_5.png" /></figure>

This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 764048.
## Document tracks

<table><tr><td>Identification</td><td>POLYPHEM_D4.3Control system design</td></tr><tr><td>TITLE OF DELIVERABLE</td><td>Report on the control system design</td></tr><tr><td>Author(s)</td><td>F. Pithoud, J. Roschen, R. Aumann</td></tr><tr><td>Reviewers(s)</td><td>Alain Ferriere, Simon Schütrumpf</td></tr><tr><td>Related Work Package (s)</td><td>WP4: System Integration and overall plant design</td></tr><tr><td>Beneficiary responsible of delivery</td><td>CNRS</td></tr><tr><td>Due date of delivery</td><td>30/11/2021</td></tr><tr><td>Actual date of submission/revision</td><td>01/09/2022</td></tr><tr><td>Number of pages</td><td>30</td></tr><tr><td>SUMMARY</td><td>This document is the deliverable D4.3 of the project POLYPHEM. It is planned in the framework of the Work Package 4 (System integration and overall plant design). The report presents the principles of the design of the control system of the plant, the management of the various operation modes including emergency situations, and the interactions between the different controllers.</td></tr><tr><td>Dissemination level</td><td>Confidential (CO)</td></tr><tr><td>Repository</td><td>https://dms.POLYPHEM-project.eu</td></tr></table>

## Document History and Validation

<table><thead><tr><td>Date</td><td>Name</td><td>Status</td></tr></thead><tbody><tr><td>15/02/2021</td><td>Frédéric Pithoud</td><td>Creation</td></tr><tr><td>02/03/2021</td><td>Alain Ferriere</td><td>Review 1</td></tr><tr><td>08/04/2021</td><td>Simon Schütrumpf</td><td>Review 2</td></tr><tr><td>29/08/2022</td><td>Alain Ferriere</td><td>Final</td></tr></tbody></table>

All information in this document only reflects the author's view. The European Commission is not responsible for any use that may be made of the information it contains.
## Background: about the POLYPHEM project

<table><tr><td>FULL TITLE</td><td>SMALL-SCALE SOLAR THERMAL COMBINED-CYCLE</td></tr><tr><td>Acronym</td><td>POLYPHEM</td></tr><tr><td>Call identifier</td><td>H2020 LCE-07-2017-RES-RIA-TwoStage</td></tr><tr><td>Instrument</td><td>Research and Innovation Action (RIA)</td></tr><tr><td>Grant Agreement N°</td><td>764048</td></tr><tr><td>Starting Date</td><td>01/04/2018</td></tr><tr><td>Duration</td><td>48 months</td></tr><tr><td>Website</td><td>https://www.POLYPHEM-project.eu</td></tr><tr><td>Keywords</td><td>Renewable electricity; Energy collection, conversion and storage; Renewable energy</td></tr><tr><td>Additional keywords</td><td>Concentrated solar power; Solar tower system; Combined cycle; Gas-turbine; Thermal energy storage; Organic Rankine cycle; Process control</td></tr><tr><td>Beneficiaries</td><td>CNRS, CEA, CIEMAT, Arraela S.L., Fraunhofer ISE, Kaefer Isoliertechnik, Orcan Energy, Euronovia, Aalborg CSP</td></tr></table>

The POLYPHEM project is a research and innovation action funded by the European Union's H2020 program. It is implemented by a European consortium of 4 research centres and 5 industrial partners. The aim is to increase the flexibility and improve the performance of small solar tower power plants. The concept of POLYPHEM consists in implementing a combined cycle formed by a solarized micro gas-turbine and a Rankine organic cycle machine, with an integrated thermal storage device between the two cycles. The need for cooling is minimal.

Developed from a patented technology by CNRS and CEA, the pressurized air solar receiver is integrated in the micro-turbine cycle. The thermal efficiency targeted for the receiver is 80% with a cost of 400 €/kW. The innovative thermal storage uses a thermal oil and a single thermocline tank with a technical concrete filler material.

The main expected impact of this project is to enhance the competitiveness of low-carbon energy production systems through the technology developed. The expected progress is a better fitting of electricity generation to variable local needs, an overall conversion efficiency of solar energy into electricity of 18% for an investment cost of less than 5 €/W and a low environmental impact. By 2030, the cost of electricity production targeted by the POLYPHEM technology is 165 €/MWh for an annual direct normal irradiation of 2600 kWh/m²/year (North Africa and Middle East) and 209 €/MWh under 2050 kWh/m²/year (Southern Europe). In addition to decentralized power generation, other applications are considered for the deployment of this technology used in poly-generation: industrial heat production, solar heating and cooling, desalination of seawater or brackish water.

A prototype plant of 60 kWel with a thermal storage of 1300 kWh is designed, built and installed on the site of the experimental solar tower of Themis in Targasonne (France). The objective of the project is to validate the technical choices under test conditions representative of actual operating conditions.

*This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 764048*
## Table of content

<table><tr><td>1. SUMMARY</td><td>6</td></tr><tr><td>2. CONTROL SYSTEM OF THE POLYPHEM PLANT: INITIAL DESIGN</td><td>6</td></tr><tr><td>2.1 General information</td><td>6</td></tr><tr><td>2.1.1 Network and VLANs</td><td>7</td></tr><tr><td>2.1.2 Concept diagram of the THEMIS plant</td><td>9</td></tr><tr><td>2.1.3 P&amp;ID</td><td>9</td></tr><tr><td>2.2 Equipments dedicated to the control</td><td>12</td></tr><tr><td>2.3 Detail of the control system design by perimeter</td><td>12</td></tr><tr><td>2.3.1 Control of the air circuit</td><td>12</td></tr><tr><td>2.3.2 Control of the oil circuit</td><td>15</td></tr><tr><td>2.3.3 Control of the ORC</td><td>19</td></tr><tr><td>3. CONTROL OF THE PLANT: FINAL DESIGN</td><td>21</td></tr><tr><td>3.1 General information</td><td>21</td></tr><tr><td>3.1.1 Final P&amp;ID</td><td>22</td></tr><tr><td>3.1.2 Network &amp; VLAN</td><td>23</td></tr><tr><td>3.1.3 Control design of the oil loop</td><td>23</td></tr><tr><td>4. CONCLUSION</td><td>27</td></tr><tr><td>5. ANNEX</td><td>29</td></tr><tr><td>5.1 Table of operation modes of Gas Turbine</td><td>29</td></tr><tr><td>5.2 Initial version of P&amp;ID</td><td>30</td></tr></table>

## List of Figures

<table><tr><td>Figure 1: Network architecture &amp; VLANs</td><td>7</td></tr><tr><td>Figure 2: Concept diagram of the THEMIS plant</td><td>9</td></tr><tr><td>Figure 3: P&amp;ID - Top air circuit</td><td>10</td></tr><tr><td>Figure 4: P&amp;ID - Oil loop</td><td>11</td></tr><tr><td>Figure 5: State Diagram of the turbine/generator</td><td>13</td></tr><tr><td>Figure 6: Transient configurations</td><td>16</td></tr><tr><td>Figure 7: Final version of the P&amp;ID of the POLYPHEM prototype plant</td><td>22</td></tr><tr><td>Figure 8: CNRS control cabinet</td><td>24</td></tr><tr><td>Figure 9: HMI of the POLYPHEM SCADA</td><td>28</td></tr><tr><td>Figure 10: Initial version of the P&amp;ID of POLYPHEM prototype plant</td><td>30</td></tr></table>
List of Acronyms and Abbreviations

<table><thead><tr><td>Acronym/abbreviation</td><td>Meaning/full text</td></tr></thead><tbody><tr><td>EES</td><td>Engineering Equation Solver (software tool)</td></tr><tr><td>HMI</td><td>Human-Machine Interface</td></tr><tr><td>HTF</td><td>Heat Transfer Fluid</td></tr><tr><td>NIST</td><td>National Institute of Standards and Technology</td></tr><tr><td>ORC</td><td>Organic Rankine Cycle</td></tr><tr><td>P&ID</td><td>Piping & Instrumentation diagram</td></tr><tr><td>PLC</td><td>Programmable Logic Controller</td></tr><tr><td>PT</td><td>Platinum Resistance Temperature Detector</td></tr><tr><td>REFPROP</td><td>Reference Properties (database)</td></tr><tr><td>RHX</td><td>Recovery Heat Exchanger</td></tr><tr><td>SCADA</td><td>Supervisory Control and Data Acquisition</td></tr><tr><td>TC</td><td>Thermocouple</td></tr><tr><td>TCP</td><td>Transmission Control Protocol</td></tr><tr><td>TCP/IP</td><td>Transmission Control Protocol/Internet Protocol</td></tr><tr><td>TES</td><td>Thermal Energy Storage</td></tr><tr><td>VLAN</td><td>Virtual Local Area Network</td></tr></tbody></table>
# 1. SUMMARY

In agreement with all partners, CNRS PROMES holds the general information on the oil circuit and is at the interface with all partners: KAEFER, CIEMAT, CEA, AALBORG and ORCAN.

CNRS PROMES is in charge of the general control design and will develop the acquisition and control of the THEMIS plant. Each partner is responsible of the right operation of their perimeter.

The control system design addresses the following challenges:

- How to operate the plant efficiently and safely in various modes (filling, draining, storage charging/discharging, maximum or on-demand power generation...)

- Communication between controllers and actuators/sensors

The report deals with all the circuits:

- the top cycle with the air receiver, the turbine & the heat exchanger located at the top of the tower

- the thermal oil circuit making the junction between the top and bottom cycle

- the bottom cycle with the ORC and the thermal energy storage

This report presents a general description of the control system. The logics which are integrated in each PLC remain internal ownership.

# 2. CONTROL SYSTEM OF THE POLYPHEM PLANT: INITIAL DESIGN

## 2.1 GENERAL INFORMATION

The control system of POLYPHEM is carried out by the following actors:

- KAEFER in charge of the top air cycle with the air intake/exhaust, the compressor/turbine

- CNRS in charge of the HTF (thermal oil) circuits (top & bottom)

- ORCAN in charge of the ORC

The control system is composed of 4 Programmable Logic Controllers (PLC), each of them being designed and supplied by a specific partner: KAEFER designs and supplies the control of the gas-turbine, CNRS designs and supplies the control of the oil circuits and ORCAN designs and supplies the control of the ORC. The control of the heliostat field, which is covered by CNRS, already exists. The interaction between this latter and the other controllers is considered in the present work.

The PLCs interact jointly for the right operation of the plant.

The controller of the gas-turbine:

- Manages the start-up and stop of the machine

- Regulates the rotation speed of the compressor

- Controls the air pressure and air temperature at the inlet of the solar receiver

- Controls the electrical power generated and the heat directed to the top heat exchanger

- Guarantees the safety of its perimeter

The controller of the HTF circuits:

- Manages the filling/draining of the circuits

- Regulates the pumps and valves to fulfil the requirement of heat transfer from the top to the bottom cycle
- Controls the charging/discharging of the TES at the temperature set.

- Guarantees the safety of the components

The controller of the ORC:

- Manages the start-up and stop of the ORC

- Regulates the ORC to fulfil the required power generation

- Guarantees the cooling of the oil to enable full charging of the TES.

- Guarantees the safety of the ORC

The controller of the solar field:

- Manages the focusing/defocusing of heliostats on the solar receiver in order to deliver the required solar power

- Defocuses the concentrated solar beam from the receiver in situation of emergency

### 2.1.1 Network and VLANs

Partners will interact during experiments at the THEMIS plant through a dedicated network presented with the figure below.

<figure><img src="image_6.png" /><figcaption>Figure 1: Network architecture & VLANs</figcaption></figure>

The figure "Network architecture & VLANs" is decomposed in terms of:

- VLANs: Polyphem Network, THEMIS network, Private VLAN

- locations: top tower, bottom tower, heliostat field, administration building

#### 2.1.1.1 VLAN

The Figure 1 indicates in the legend that 3 VLANs compose the network at THEMIS. The "THEMIS network" (red line in Figure 1) exists, it was created for previous purposes. This network gives full access to the laboratory PROMES and will be provided only for CNRS's personals.
A secured network called "Private VLAN" (light blue line in Figure 1) is created in order to protect the network architecture at CNRS PROMES. Partners will get access to this network to connect remotely and for internet connection on site.

The VLAN called "POLYPHEM network" (purple line in Figure 1) serves to transfer data to and from the process to and from the various PLCs. Each command and each data acquired goes through this network.

### 2.1.1.2 Location

The following equipment are installed at the top of the tower:

- KAEFER'S PLC

The programmable logic controller ensures that the air perimeter is working the right way

- KAEFER'S Gateway

This module ensures the exchange of data between two different protocols (Profinet TCP and Modbus TCP)

- CNRS' PLC

This PLC makes the data acquisition and the command of all the equipment of the oil circuit at the top of the tower. It also includes the measurement on the solar receiver. Data are sent to the POLYPHEM office through the "THEMIS network" presented in 2.1.1.1 au-dessus.

- Network cables

CNRS provides all Ethernet cables used for the experimentation. It includes the links from the switch #1 to the gateway, to KAEFER'S PLC, and to CNRS's PLC.

- Switch #1

The industrial unmanaged gigabit switch #1 at the top of the tower ensures the right communication between all participants (KAEFER, CNRS) and between the HMI in the administration building and the equipment at the top of the tower.

- Emergency stop button

An emergency button is commanded by KAEFER and CNRS on specific procedure. Alarms are configured and established by partners to defocus the heliostat and protect the circuit from overheating.

The following equipment are installed on the ground at the bottom of the tower:

- ORCAN'S PLC

The PLC ensures the right operation of the Organic Rankine Cycle.

- CNRS'S PLC

This PLC makes the data acquisition and the command of all the equipments of the oil circuit at the bottom of the tower. It ensures the right operation of the oil loop and the right interface with ORCAN.

- Switch #2

The industrial unmanaged gigabit switch #2 makes the link between the switch #1 connected with Ethernet cable and the switch #3 connected with optical fiber.

- Network cables
CNRS provides all ethernet cables used for the experimentation. It includes the links from the switch #2 to ORCAN's PLC, to CNRS's PLC, the ethernet cable from the switch #1 to the switch #2. The optical fiber from the switch #2 to the switch #3 exists.

The following equipment are installed in the administration building:

- Switch #3, #4, #5 and #6

The switch #3 and #4 cover the POLYPHEM network. The switch #5 and #6 cover the private VLAN. These switch makes the connection from the HMIs to the specific network.

- HMIs

The HMIs of CNRS, KAEFER and ORCAN are installed in the POLYPHEM office located in the administration building. Therefore, each partner manages its specific PLC.

### 2.1.2 Concept diagram of the THEMIS plant

The general diagram of the plant is presented below for a better understanding of the control system design.

<figure><img src="image_7.png" /><figcaption>Figure 2: Concept diagram of the THEMIS plant</figcaption></figure>

### 2.1.3 P&ID

The process flow diagram is decomposed in 2 documents. The first one presents the top air circuit and the second one the oil loop with the primary & secondary oil circuits. The P&ID was revised by an engineering service company subcontracted by CNRS. The P&ID indicates:

- sensors type and location

- actuators type and location

- a specific color of line is allocated to each type of circuit

A comprehensive description of the P&ID is found in the deliverable D4.2 "Report on the general engineering" dated on 08/07/2022
P&ID of the top air circuit:

<figure><img src="image_8.png" /><figcaption>Figure 3: P&ID – Top air circuit</figcaption></figure>
P&ID of the oil loop:

<figure><img src="image_9.png" /><figcaption>Figure 4 : P&ID – Oil loop</figcaption></figure>
## 2.2 EQUIPMENTS DEDICATED TO THE CONTROL

The architecture of a control system is composed of an HMI, a controller, sensors and actuators.

The HMI acquires and saves data from sensors and reacts to them through logics integrated in the HMI. Then, orders are sent from the HMI to the dedicated controller in order to command the specific equipment. This order follows a protocol which is the basis of communication between the HMI and the controller.

Regarding the POLYPHEM experiment, several controllers will be implemented.

- The first one in the POLYPHEM office for emergency situations with an emergency button.

- 2 controllers at the bottom of the tower. 1 in the perimeter of the CNRS for acquisition and command. 1 in the perimeter of ORCAN.

- 2 controllers at the top of the tower. 1 in the perimeter of the CNRS for acquisition and command. 1 in the perimeter of KAEFER to manage the turbine.

If the communication protocol is different between partners, a gateway needs to be installed as two different languages can't react together. KAEFER PLC's protocol is based on Profinet TCP (cf. Figure 2) which is a different protocol compared to CNRS, Modbus TCP. The Modbus TCP protocol used in intern at the CNRS PROMES has brought already a good satisfaction. The product originates generally from WAGO.

Then a gateway has to be installed on KAEFER's PLC in order to allow communication and exchange information with CNRS. ORCAN decided to use Modbus TCP to facilitate the communication with CNRS, without any need for gateways.

For the right operation of the plant, control of valves/pumps, setpoint configuration, safety situations, data need to be exchanged between partners. **A table of exchange data** summarizes all data shared by partners, the format of the data, the connection ID.

Regarding the CNRS's HMI, the interface is developed under Labview for the data acquisition and command of the equipments of the oil circuit.

## 2.3 DETAIL OF THE CONTROL SYSTEM DESIGN BY PERIMETER

### 2.3.1 Control of the air circuit

#### 2.3.1.1 Design point

Design points considered on the air circuit are the following:

- Speed at the turbine: 52000 rpm

- Speed at the generator: 2975 rpm

- Air outlet temperature on the compressor: 190 °C

- Compressor discharge pressure (absolute): 3.32 bar

- Air inlet temperature in the solar receiver: 190 °C

- Air outlet temperature in the solar receiver: 750 °C

- Air inlet temperature in the turbine: 750 °C

- Air outlet temperature in the turbine: 495 °C

- Air inlet temperature in the recovery heat exchanger: 495 °C

- Air outlet temperature in the recovery heat exchanger: 133 °C

#### 2.3.1.2 Transient regimes

##### Start-up

During normal operation transient regimes of the turbine are the start-up and the shut-down.
In the beginning of the start-up procedure the turbine is started via generator in motor operation and accelerated to 1,600 rpm generator speed which is about 53% of nominal speed. In this operation point the mass flow and pressure of the air is reduced. As there is no heat source (no heliostats focused on solar receiver) within the turbine process the compression power is provided by the generator in motor mode.

In the next step a certain number of heliostats is focused on the receiver. As a result, the turbine inlet temperature increases and the generator power in motor mode decreases. The number of focused heliostats shall be increased until a decreased generator power in motor mode is reached.

If a defined generator power is reached the system turns over to a constant power control mode.

In this mode the speed is controlled to hold the power constant. If then the solar power increases, also the speed increases up to the nominal speed. This is 2,950 rpm for the generator and 52,000 for the turbine.

The number of focused heliostats increase until the nominal power of the generator (40 kW in generator mode) is reached.

## Shut down

The shutdown process corresponds to the start-up procedure in reverse order.

## Load Modulation

The turbine speed is constant over all load levels. The modulation of the load is done by the modulation of the turbine inlet temperature. The turbine inlet temperature is controlled by the amount of solar power.

<figure><img src="image_10.png" /><figcaption>Figure 5: State Diagram of the turbine/generator</figcaption></figure>
The States of the turbine/generator system are shown in Figure 5. A more detailed explanation of the states 1 to 10 is given in the table in the appendix.

### 2.3.1.3 Emergency situation

Emergency situations are organized in terms of type of event which could occurs.

The following events are considered as emergency situations and in the development of the safety logics:

- Leakage from the air circuit

- Fire declaration

- Malfunction of sensors

- False values sent to the HMI

- Loss of sensors

- Malfunction of actuators

- Valve/Pump not operating or not the right way

- Loss of electric Power

- Exceeding limits of the plant

- Pressure

- Temperature

- Mass flow

- Expansion of oil

<table><thead><tr><td>Event</td><td>Carry out a turbine shutdown</td><td>Defocus heliostats</td><td>Opening the RHX bypass</td></tr></thead><tbody><tr><td>Overheat of oil in RHX</td><td>If bypass opening fails</td><td>If bypass opening fails</td><td>immediately</td></tr><tr><td>Overheat of the solar receiver</td><td>After cooling down</td><td>immediately</td><td>-</td></tr><tr><td>Leakage</td><td>immediately</td><td>immediately</td><td>-</td></tr><tr><td>Overheat of the load bank</td><td>immediately</td><td>immediately</td><td>-</td></tr><tr><td>Implausible sensor values</td><td>immediately</td><td>immediately</td><td>-</td></tr><tr><td>Operation near surge</td><td>immediately</td><td>immediately</td><td>-</td></tr><tr><td>Trouble with the lubrication</td><td>immediately</td><td>immediately</td><td>-</td></tr><tr><td>Loss of electric Power</td><td>immediately</td><td>immediately</td><td>-</td></tr><tr><td>Open RHX bypass command from CNRS</td><td>-</td><td>-</td><td>immediately</td></tr><tr><td>Turbine shutdown command from CNRS</td><td>immediately</td><td>Carried out from CNRS</td><td>-</td></tr></tbody></table>

### Emergency Shut-down of the turbine

An emergency shutdown follows the defocusing of all heliostats, the opening of a waste gate valve to significantly reduce the mass flow through the turbine and a ramp down operation of the generator and
turbine. To pretend damage of the turbine by overheated lubrication oil the lubrication system continuous
to work for about 30 minutes.

By-passing RHX

In case of overtemperature the Bypass of the RHX will be opened immediately to protect the oil from overheating. There will be two signals in the KAEFER control system to determine if the oil temperature is inside the allowed range. One sensor will be evaluated by the KAEFER control system and another sensor will be evaluated by the CNRS control system and sends a release signal if the temperature is inside its limits. If the signal drops, in case the temperature is outside limits, or the wire breaks the KAEFER control system react with the emergency procedure

If there occurs a failure at the valve by-passing the RHX a shut-down of the turbine will be initiated. Following the shut-down procedure also the waste gate will be opened. This leads to a fast and significant drop of the RHX air inlet temperature to protect the thermal oil.

Interface to CNRS control system

The Interface to the CNRS control System consists of digital in- and outputs.

For every level of emergency, a in/output will be defined. This signal will be defined that no emergency is a
logical 1 and emergency is a logical 0 so the system is safe for wire break.

2.3.2 Control of the oil circuit

The P&ID is decomposed in 2 branches of oil:

- the oil circuit making the link between the bottom tower and the top of the tower

- the filling and draining circuit

CNRS PROMES is responsible of all the perimeter on the oil loop (instrumentation, equipments). TES and ORC
are not considered in this perimeter and are points of interface.

2.3.2.1 Design point

Simulations with the Epsilon® simulation software were undertaken by Fraunhofer with the previous P&ID (Annex 4.2) and exposed in the deliverable 4.1 in order to obtain design points. Revisions to the design conditions brought the following modifications of:

- entries on maximum temperature that could be seen by the oil

- operating modes

Design points considered on the primary oil circuit are the following:

- Air inlet on the top heat exchanger: 495°C

- Air outlet on the top heat exchanger: 133°C

- Oil inlet on the top heat exchanger: 129°C

- Oil outlet on the top heat exchanger: 333°C

- Mass flow rate on the top heat exchanger: 0.675 kg/s
Design points considered on the secondary oil circuit are the following:

- Oil inlet (primary circuit) on the bottom heat exchanger: 331.5°C

- Oil outlet (primary circuit) on the bottom heat exchanger: 130°C

- Oil inlet (secondary circuit) on the bottom heat exchanger: 113°C

- Oil outlet (secondary circuit) on the bottom heat exchanger: 323°C

- Mass flow rate on the bottom heat exchanger: 0.659 kg/s

It is important to note that the process of the plant will rely mostly on off-design point. Off-design are not emergency situations but is the range of use of the plant. The process will be mapped from minimum load to maximum load. On this range of load, several off-design points of the process will be scanned.

### 2.3.2.2 Transient regimes

The following transient regimes are considered:

- empty circuits to filling or from filling to draining

- starting event to stabilized situation

- setpoint modification within a given operating mode

- the modification of an operating mode

The diagram below explains the upper description.

<figure><img src="image_11.png" /><figcaption>Figure 6: Transient configurations</figcaption></figure>

Transient regimes are regulated by P&ID regulations to reach an established profile based on a fixed setpoint.

#### Empty circuits to filling or from filling to draining

At the launch of the plant either for the first run (circuits empty in oil) either after a complete draining of the system, the filling pump will be commanded and controlled on the value given by the level transmitter in the
expansion vessel. After the reach of the minimum or a specific value in the expansion vessel, the filling is stopped.

**Starting event to stabilized situation**

After the filling in oil of the circuits, an operating mode is imposed with a specific setpoint.

The 2 circuits (primary and secondary) are equipped with a pump in order to ensure an exchange of heat and to reach the designed mass flow rate.

The 2 pumps will be commanded in order to reach the setpoint entered by the user of the plant and regulated on the temperature at the outlet of the heat exchanger.

**Setpoint modification**

The P&ID regulations reacts in order to reach the setpoint.

**Switch from an operating mode to another one**

Regarding the discharge mode or load of the TES and discharge through the ORC simultaneously, 3-way valves on the secondary circuit are commanded. Their operations are controlled in order not to exceed the maximum temperature at the inlet of the ORC which is 170°C.

Regarding the load of the TES, temperature at the outlet of the secondary heat exchanger are monitored upon the inlet power of the top heat exchanger. The electrical heater could be operated as an overheat source to reach a desired temperature at the inlet of the TES superior to the capacity of the plant in full solar.

**2.3.2.3 Emergency situation**

Emergency situations are organized in terms of type of event which could occur.

The following events are considered as emergency situations and in the development of the safety logics:

- Leakage in the air circuit which could impact the oil circuit

- Leakage in the oil circuit

- Fire declaration

- Malfunction of sensors

- False values sent to the HMI

- Loss of sensors

- Malfunction of actuators

- Valve/Pump not operating or not the right way

- Exceeding limits of the plant

- Pressure

- Temperature

- Mass flow

- Expansion of oil

For each operating mode, a failure tree is built according to the events presented above.

Then, depending on the seriousness of the event, different level of safety procedure: low, intermediate, high will be integrated in the logics. Some examples are presented below:
**High safety logic:**

- Overheating of the solar receiver:

<figure><img src="image_12.png" /></figure>

- Dramatic oil leakage:

<figure><img src="image_13.png" /></figure>

**Intermediate safety logic:**

- Overheating of oil in RHX:

<figure><img src="image_14.png" /></figure>

**Low safety logic:**

- Low temperature in the oil tank (< 25°C)

Under low ambient temperature (typically in winter), the viscosity of the oil in the oil tank drops down to very low value. The preheating of the oil in the tank is required before the filling of the circuits can be started.
### 2.3.3 Control of the ORC

#### 2.3.3.1 Design point

The ORC simulations were carried out using EES software with REFPROP library (from NIST) for determining the fluid properties. To be able to handle this design points for oil and refrigerant some modifications in the PLC of the ORC have been necessary compared to the existing series product.

Design points considered on the oil circuit are the following:

- Oil inlet (secondary circuit): 170°C

- Oil outlet (secondary circuit): 119°C

- Mass flow rate oil: 4.3 kg/s

Design points considered on the ORC (R1233zde) circuit are the following:

- Live vapor temperature: 140°C

- Heat input: 435 kW

- Net electric output: 34,9 kW

- Mass flow rate refrigerant: 1.8 kg/s

#### 2.3.3.2 Transient regimes

The ORC System uses a PLC System from B&R (now ABB) which is from the hardware point of view very similar to Orcan's series product. Software and control parameters have been subject to modifications for the Polyphem Project.

The ORC has five different operation modes. They are shown on the display and are also communicated via Modbus TCP.

<figure><img src="image_15.png" /></figure>

System mode indication:

0: Off

1: Standby

2: Start

3: Control mode

4: Shutdown

5: Service

**Mode 0 = Off:** Required Thermal Oil temperature: <105 °C

In the mode 0 the ORC is off. That means it is switched off via panel, via remote access (Orcan) or via the Modbus TCP connection (operation enable signal from superior site controller).

**Mode 1 = Standby:** 105 °C < Required Thermal Oil temperature < 140 °C (steadily controlled output signal)

If temperature of 105 °C is not exceeded although the control signal wishes a higher temperature the ORC will wait in Mode 1 (Standby) for temperature to rise.
In mode 1, the ORC starts to check all necessary parameters to secure that start up is possible (e.g. proper parameters of electric grid (between frequency and voltage limits, proper condition of the ORC system itself and external temperatures of input ambient etc.). These checks are constantly carried out in all operation modes 1 to 4.

**Mode 2 = Start: 105 °C < Required Thermal Oil temperature < 140 °C (steadily controlled output signal)**

In mode 2, the ORC begins to start if the temperature of the oil inlet is high enough. Usually the start needs about 1 minute.

**Mode 3 = Normal operation I mode: 140 °C < Required Thermal Oil temperature < 170 °C (steadily controlled output signal)**

In mode 3, the ORC is operating according to the set points that have been selected in the PLC system. As long as thermal oil temperature does permit, the ORC system tries to reach the maximum electric output power and control the thermal oil temperature at the inlet of the ORC in order to not to run into overload. Manually lower thermal oil input set point temperatures can be selected in order to limit at the same time the consumption of thermal power and electric output.

**Mode 4 = Shutdown: 105 °C < Required Thermal Oil temperature < 140 °C (steadily controlled output signal)**

In case of too low temperature in the supply line, the ORC will switch in mode 4 and ORC will shut down. The ORC also shuts down if the operation "enable" signal via Modbus TCP is removed. Mode 4 is also possible if there are problems (warnings or errors) or if the emergency button on the electrical cabinet is pressed (emergency shutdown). Time for normal shutdown is about 2-3 minutes. In case of an emergency shutdown it needs still few seconds.

After the shutdown the ORC itself switches to mode 0 and waits for 360 s. After 360 s it will start with mode 1 again itself. Only if there are errors which don't allow a further operation it won't start itself.

**Mode 5 = Service:**

This mode could be necessary for the Orcan Service team.

More details are described in the operating manual.

#### 2.3.3.3 Emergency situation

There are different operation conditions which will be indicated for the ORC as emergency:

**General:**

Emergency button on the electric cabinet → emergency shutdown

**ORC circuit:**

Pressure higher than 23,5 bar → feed pump switches off

Pressure higher than 24,1 bar → bypass in ORC opens

Pressure higher than 24,5 bar → critical process error (shutdown)

Pressure higher than 26 bar → safety valve in ORC opens

Temperature live vapor higher than 145 °C → critical process error (shutdown)

**Oil circuit:**

Temperature higher than 180 °C → safety temperature limiter (STB) causes valve V202 to open and valve V201 to close (bypass of the ORC)
Pressure higher than 11 bar → safety valve (S201) opens

<figure><img src="image_16.png" /></figure>

# 3. CONTROL OF THE PLANT: FINAL DESIGN

## 3.1 GENERAL INFORMATION

Major issue occurred in summer 2021 in the final step of the manufacturing of the solar receiver. The solar receiver cannot be delivered. It was decided that the receiver and the gas-turbine will not be installed on site. The heat source consists of a burner which delivers hot air to the recovery heat exchanger. These components are installed on the ground at the bottom of the tower. The P&ID was revised accordingly. Consequently, the control system was also modified. The final design of the control system of the plant is presented in this section.
### 3.1.1 Final P&ID

The final P&ID is presented in Figure 7. It is also found in the deliverables D6.1 & D4.2

<figure><img src="image_17.png" /><figcaption>Figure 7: Final version of the P&ID of the POLYPHEM prototype plant</figcaption></figure>
### 3.1.2 Network & VLAN

The network diagram was realized by CNRS in order to ensure the right communication from the POLYPHEM office to each equipment which needs to communicate.

At the bottom of the tower, it was installed a patch headband to shuffle network cables. Connected to the patch headband, it can be found the network cable in category 7 S/FTP PE from the top of the tower and the rest of the equipment which communicate at the bottom of the tower with network cables in cat 6 F/UTP LSOH.

The switch #2 finally ensures the communication from the administration building to the right equipment. Then, data are sent from the network room in the administration building to the right network port RJ45 in the POLYPHEM office.

<figure><img src="image_18.png" /></figure>

### 3.1.3 Control design of the oil loop

The thermal process is regulated. The regulated actuators and their input signals are indicated in the final P&ID presented in Figure 7.

To sum up:

- P-01 is regulated over the oil temperature TT-01 at the outlet of the RHX
- EV-02 is regulated over the oil temperature TT-05 at the inlet of the ORC

- P-ORC-01 is regulated over the oil temperature TT-07 at the suction side of the main pump P-01

- The fan is regulated over the average air temperature TT-Air-00 & TT-Air-05 at the outlet of the burner.

### 3.1.3.1 PLC

CNRS designed and fabricated the PLC, with subcomponents supplied by WAGO. The PLC communicates in Modbus TCP/IP. CNRS has a long-term experience with this technology.

### 3.1.3.2 Control cabinet

Below is presented the diagram of the control cabinet.

<figure><img src="image_19.png" /><figcaption>Figure 8: CNRS control cabinet</figcaption></figure>

The control cabinet is equipped with the following WAGO modules:

<table><thead><tr><td>Module type</td><td>Ref</td><td>Channels quantity</td></tr></thead><tbody><tr><td>PLC</td><td>750-891</td><td>NA</td></tr><tr><td>TC</td><td>750-458</td><td>96</td></tr><tr><td>PT100</td><td>750-450</td><td>12</td></tr><tr><td>Polarity distribution - 24V</td><td>750-1605</td><td>16</td></tr><tr><td>Polarity distribution - 0V</td><td>750-1606</td><td>16</td></tr><tr><td>Digital input - 24VDC</td><td>750-402</td><td>8</td></tr></tbody></table>
<table><tr><td>Digital output – 24VDC</td><td>750-504</td><td>16</td></tr><tr><td>Analog output – 4-20 mA</td><td>750-555</td><td>8</td></tr><tr><td>Analog input – 4-20 mA</td><td>750-454</td><td>14</td></tr></table>

### 3.1.3.3 Correspondence between WAGO module to measurements

#### 3.1.3.3.1 Module Thermocouple – 750-458

The table below is composed of thermocouple of type J and K, respectively in blue and black.

<table><thead><tr><th>750-458</th><th>Module #1</th><th>Module #2</th><th>Module #3</th><th>Module #4</th><th>Module #5</th><th>Module #6</th><th>Module #7</th><th>Module #8</th><th>Module #9</th></tr></thead><tbody><tr><td>Channel #1</td><td>T01</td><td>T25</td><td>T73</td><td>T124</td><td>T172</td><td>T223</td><td>T261</td><td>TW1</td><td>TW9</td></tr><tr><td>Channel #2</td><td>T02</td><td>T26</td><td>T81</td><td>T125</td><td>T173</td><td>T224</td><td>T271</td><td>TW2</td><td>TW10</td></tr><tr><td>Channel #3</td><td>T03</td><td>T31</td><td>T91</td><td>T126</td><td>T181</td><td>T225</td><td>T274</td><td>TW3</td><td>TW11</td></tr><tr><td>Channel #4</td><td>T11</td><td>T41</td><td>T101</td><td>T131</td><td>T191</td><td>T226</td><td>T281</td><td>TW4</td><td>TW12</td></tr><tr><td>Channel #5</td><td>T21</td><td>T51</td><td>T111</td><td>T141</td><td>T201</td><td>T231</td><td>T291</td><td>TW5</td><td>TW13</td></tr><tr><td>Channel #6</td><td>T22</td><td>T61</td><td>T121</td><td>T151</td><td>T211</td><td>T241</td><td>T294</td><td>TW6</td><td>TW14</td></tr><tr><td>Channel #7</td><td>T23</td><td>T71</td><td>T122</td><td>T161</td><td>T221</td><td>T251</td><td>T301</td><td>TW7</td><td>TD1</td></tr><tr><td>Channel #8</td><td>T24</td><td>T72</td><td>T123</td><td>T171</td><td>T222</td><td>T254</td><td>T311</td><td>TW8</td><td>TD2</td></tr></tbody></table>

<table><thead><tr><th>750-458</th><th>Module #10</th><th>Module #11</th><th>Module #12</th></tr></thead><tbody><tr><td>Channel #1</td><td>TB1</td><td>TT_Air_01</td><td>TT_amb_in</td></tr><tr><td>Channel #2</td><td>TB2</td><td>TT_Air_02</td><td>TT_amb_ext</td></tr><tr><td>Channel #3</td><td>TB3</td><td>TT_Air_03</td><td>-</td></tr><tr><td>Channel #4</td><td>TB4</td><td>TT_Air_04</td><td>-</td></tr><tr><td>Channel #5</td><td>TB5</td><td>TT_Air_00</td><td>-</td></tr><tr><td>Channel #6</td><td>TB6</td><td>TT_Air_05</td><td>-</td></tr><tr><td>Channel #7</td><td>TF1</td><td>TT_RHXSkin</td><td>-</td></tr><tr><td>Channel #8</td><td>TF2</td><td>TT_RHX_ext</td><td>-</td></tr></tbody></table>
### 3.1.3.3.2 Module PT100 - 750-450

<table><thead><tr><th>750-450</th><th>Module #1</th><th>Module #2</th><th>Module #3</th></tr></thead><tbody><tr><td>Channel #1</td><td>TT-01</td><td>TT-05</td><td>TT-09</td></tr><tr><td>Channel #2</td><td>TT-02</td><td>TT-06</td><td>-</td></tr><tr><td>Channel #3</td><td>TT-03</td><td>TT-07</td><td>-</td></tr><tr><td>Channel #4</td><td>TT-04</td><td>TT-08</td><td>-</td></tr></tbody></table>

### 3.1.3.3.3 Module digital input - 750-402

The digital input works with 24VDC.

<table><thead><tr><th>750-402</th><th>Module #1</th><th>Module #2</th></tr></thead><tbody><tr><td>Channel #1</td><td>Default P-ORC-01</td><td>Answer P-02 ON/OFF</td></tr><tr><td>Channel #2</td><td>Answer P-ORC-01 ON/OFF</td><td>Default Fan</td></tr><tr><td>Channel #3</td><td>Default P-01</td><td>Answer Fan ON/OFF</td></tr><tr><td>Channel #4</td><td>Answer P-01 ON/OFF</td><td>Emergency stop</td></tr></tbody></table>

- « Default » gives the status on the circuit breaker on the line considered. If 24V is present, the circuit breaker is on meaning the equipment is fed electrically.

- « Answer » means that the relay commanded by CNRS is actually commanded. If 24V is present, the equipment is activated.

- Regarding the channel #4, the emergency stop button is read in order to signal it to the SCADA.

### 3.1.3.3.4 Module digital output - 750-504

The digital output in 24VDC commands electrical relays which feed electrical the equipment.

<table><thead><tr><th>750-504</th><th>Module #1</th><th>Module #2</th><th>Module #3</th></tr></thead><tbody><tr><td>Channel #1</td><td>P-ORC-01</td><td>Burner</td><td></td></tr><tr><td>Channel #2</td><td>P-01</td><td>Green light</td><td></td></tr><tr><td>Channel #3</td><td>P-02</td><td>Orange</td><td></td></tr><tr><td>Channel #4</td><td>Fan</td><td>-</td><td></td></tr><tr><td>Channel #5</td><td>EV-01</td><td>X</td><td>X</td></tr><tr><td>Channel #6</td><td>EV-02</td><td>X</td><td>X</td></tr><tr><td>Channel #7</td><td>EV-03</td><td>X</td><td>X</td></tr><tr><td>Channel #8</td><td>EV-Air</td><td>X</td><td>X</td></tr></tbody></table>
### 3.1.3.3.5 Module analog output - 750-555

The analog output is used to send 4-20 mA signal to the equipment controlled.

<table><thead><tr><th>750-555</th><th>Module<br>#1</th><th>Module<br>#2</th></tr></thead><tbody><tr><td>Channel #1</td><td>EV-02</td><td>P-02</td></tr><tr><td>Channel #2</td><td>P-01</td><td>-</td></tr><tr><td>Channel #3</td><td>P-ORC-01</td><td>-</td></tr><tr><td>Channel #4</td><td>Fan</td><td>-</td></tr></tbody></table>

### 3.1.3.3.6 Module analog input - 750-454

<table><thead><tr><th>750-555</th><th>Module<br>#1</th><th>Module<br>#2</th><th>Module<br>#3</th><th>Module<br>#4</th><th>Module<br>#5</th><th>Module<br>#6</th><th>Module<br>#7</th></tr></thead><tbody><tr><td>Channel<br>#1</td><td>PT-01</td><td>PT-03</td><td>PT-06</td><td>FT-01</td><td>LT-01</td><td>-</td><td>-</td></tr><tr><td>Channel<br>#2</td><td>PT-02</td><td>PT-05</td><td>PT-08</td><td>FT-02</td><td>LT-02</td><td>-</td><td>-</td></tr></tbody></table>

### 3.1.3.4 SCADA

The supervisory control and data acquisition system (SCADA) is composed of a human-machine interface (HMI) which communicates with the control cabinet and with the programmable logic controller (PLC) of the ORC group via Ethernet links. The HMI serves for the remote control of the plant, for the monitoring of the signals measured and for the recording of data files. The operation software is developed by CNRS using Labview™ environment. The actuators and sensors of the process are connected to the control cabinet via I/O terminals. Some signals supplied by the PLC of the ORC are transferred to the HMI.

## 4. CONCLUSION

The control system of the prototype plant POLYPHEM is composed of 2 controllers. Each of them controls one main circuit:

* 1 controller for the ORC circuit (bottom cycle), supplied by ORCAN, under development.

* 1 controller for the HTF

These controllers are interfaced with the thermal process through connections to measurement sensors (temperature, pressure, flowrate gauges) and to actuators (pumps and valves), using numerical communication system (network and switches) and communication protocols (Modbus). The controllers exchange information (logical signals) in order to manage start-up and stop operations and emergency situations (medium and low safety level). In addition to that, manual buttons are installed close to the process to ensure the safety of the process.

The human-machine interfaces (HMI) of the controllers will be located in a unique control room. The coordination between the operators will therefore be facilitated.

Remote access to the PLCs will be given to ORCAN from their headquarters for development or maintenance purposes (update of programme release, distance monitoring of data).
<figure><img src="image_20.png" /><figcaption>Figure 9: HMI of the POLYPHEM SCADA</figcaption></figure>
# 5. ANNEX

## 5.1 TABLE OF OPERATION MODES OF GAS TURBINE

<table><caption>Table 1: Description of the operation modes of the gas-turbine</caption><thead><tr><th>speed<br>generator/turbine</th><th>power flow<br>direction generator</th><th>Control mode</th><th>lubrication supply<br>turbine</th><th>lubrication supply gears</th><th>compressor discharge<br>temperature</th><th>compressor<br>discharge</th><th>turbine inlet<br>temperature</th><th>solar power</th><th>lubrication<br>pre-heating</th><th>lubrication<br>temperature</th><th>prelubrication<br>done</th><th>Zustand</th><th>standby/<br>rdy to</th></tr></thead><tbody><tr><td>1</td><td>0-</td><td>-</td><td>none</td><td>none</td><td>cold</td><td>atmospheric</td><td>cold</td><td>0 no</td><td>&lt;35°C</td><td>no</td><td>off/cold</td><td>no</td></tr><tr><td>2</td><td>0-</td><td>-</td><td>none</td><td>none</td><td>cold</td><td>atmospheric</td><td>cold</td><td>0 yes</td><td>&lt;35°C</td><td>no</td><td>lubrication pre-heating</td><td>no</td></tr><tr><td>3</td><td>0-</td><td>-</td><td>reduced</td><td>none</td><td>cold</td><td>atmospheric</td><td>cold</td><td>0 no</td><td>&gt;35°C</td><td>no</td><td>prelubrication</td><td>no</td></tr><tr><td>4</td><td>0-</td><td>-</td><td>reduced</td><td>none</td><td>cold</td><td>atmospheric</td><td>cold</td><td>0 no</td><td>&gt;35°C</td><td>yes</td><td>standby/rdy to start up</td><td>yes</td></tr><tr><td>5</td><td>reduced</td><td>motor operation</td><td>constant speed</td><td>nominal operation</td><td>nominal operation</td><td>reduced</td><td>greatly reduced</td><td>0 no</td><td>&gt;35°C</td><td>yes</td><td>start up</td><td>-</td></tr><tr><td>6</td><td>reduced</td><td>motor operation</td><td>constant speed</td><td>nominal operation</td><td>nominal operation</td><td>reduced</td><td>reduced</td><td>reduced</td><td>no</td><td>&gt;35°C</td><td>yes</td><td>start up</td><td>-</td></tr><tr><td>7</td><td>nominal operation</td><td>motor operation</td><td>constant speed</td><td>nominal operation</td><td>nominal operation</td><td>nominal operation</td><td>reduced</td><td>reduced</td><td>no</td><td>&gt;35°C</td><td>yes</td><td>start up</td><td>-</td></tr><tr><td>8</td><td>nominal operation</td><td>generator operation</td><td>constant speed</td><td>nominal operation</td><td>nominal operation</td><td>nominal operation</td><td>nominal operation</td><td>nominal operation</td><td>no</td><td>&gt;35°C</td><td>yes</td><td>nominal operation</td><td>-</td></tr><tr><td>9</td><td>0-</td><td>-</td><td>reduced</td><td>none</td><td>cold</td><td>atmospheric</td><td>cold</td><td>0 no</td><td>&gt;35°C</td><td>yes</td><td>relubrication</td><td>yes</td></tr></tbody></table>
5.2 INITIAL VERSION OF P&ID

<figure><img src="image_21.png" /><figcaption>Figure 10: Initial version of the P&ID of POLYPHEM prototype plant</figcaption></figure>