Decarbonization and cost reduction in industrial heating systems with electric hot oil heaters

The adoption of electric thermal oil heaters has boomed in recent years, which is in line with the general trend of electrification and decarbonization that is taking place in numerous industrial processes. The installation of an electric hot oil boiler makes it possible to decarbonize industrial heating processes operated by thermal fluid systems.

The primary reasons for this transition are economic and environmental:

  1. Electric boilers tend to have lower operational costs since they require less maintenance and do not involve handling and storing hazardous fuels. Additionally, when the price of electricity is lower than that of natural gas, operational costs decrease even further.
  2. Replacing thermal fluid heaters that operate through combustion with electric hot oil heaters contributes to the decarbonization of industrial processes. This is because boilers running on fossil fuels, such as oil or natural gas, emit carbon dioxide and other atmospheric pollutants. By replacing them with electric boilers, direct emissions of CO2 and other greenhouse gases during the heating process are avoided.

However, it’s important to note that the actual impact on decarbonization will depend on the source of electricity used to power the electric boilers. If electricity primarily comes from renewable energy sources, the contribution to decarbonization will be significant. If electricity is still mainly generated from fossil fuels, the emission reduction will be less pronounced.

The combustion heater is maintained by the customer in the following scenarios:

  • As a backup to the electric boiler.
  • As support during peak production periods.
  • When energy costs advise it.

Additional advantages of transitioning to electric hot oil boilers

In addition to the mentioned economic and environmental benefits, the implementation of electric thermal fluid boilers offers other additional advantages:

  • Electric heaters are more efficient than traditional combustion boilers, as they require less energy to achieve the same level of thermal production, reducing energy consumption and associated emissions.
  • Electric heaters reduce the emission of various pollutants. In addition to carbon dioxide, combustion boilers emit other atmospheric pollutants such as nitrogen oxides, particulates, and volatile organic compounds, which are not emitted by electric boilers.
  • They occupy less space and offer greater flexibility in terms of location since they do not require the fuel storage infrastructure associated with combustion boilers.
  • Electric boilers typically offer a higher degree of control and automation compared to combustion boilers. This allows for precise heat production adjustments based on specific needs, potentially improving efficiency.
  • The adoption of electric boilers can help companies comply with environmental regulations and avoid potential fines or penalties.

Factors to consider before replacement

When considering the replacement of a combustion thermal fluid boiler with an electric boiler, it is essential to analyze various factors to ensure that the process efficiency will achieve the desired improvements:

  • Ensure that the new heater efficiently and reliably meets the required heat demand and capacity.
  • The electric boiler should be capable of providing similar or superior performance in terms of energy-to-heat conversion.
  • Analyze investment costs and compare the operational costs of both boilers, including electricity prices and maintenance costs.
  • Availability and source of different energy sources, especially when the transition is oriented towards decarbonization.
  • Ensure that the existing electrical infrastructure can handle the additional load from the electric boiler, and significant electrical improvements are not necessary.
  • Understand regulations related to the installation and operation of electric boilers, including permits, safety standards, emissions, etc.
  • Evaluate how the electric boiler will integrate with existing heating systems and processes at the plant. Analyze how the transition to an electric boiler will affect production capacity.
  • Life cycle analysis: Consider the environmental impact throughout the life cycle of both options, from manufacturing and operation to eventual decommissioning and disposal.

The decision to replace a combustion thermal fluid boiler with an electric boiler should be based on a comprehensive assessment of these factors and identifying the option that best suits the company’s operational, economic, and environmental needs.

To do this, it is essential to collaborate with a team of engineers and consultants specialized in energy and industrial processes who can perform a thorough analysis and provide the necessary technical guidance.

Hybrid systems with parallel heaters

“Parallel boilers” or “hybrid systems” are those in which both types of boilers are used simultaneously. The parallel configuration allows for leveraging the advantages of both types of boilers to optimize the efficiency, flexibility, and reliability of the industrial heating system.

A detailed engineering analysis is essential before implementing a parallel boiler system. This involves considering the capacity and compatibility of existing boilers, available electrical infrastructure, operating costs, and the overall efficiency of the system. Proper design and careful planning will ensure that the boilers operate optimally and meet the efficiency and decarbonization goals of the industrial facility.

There are several reasons for choosing a hybrid system with parallel heaters:

  • Having both types of boilers allows for reducing operating costs, as one or the other can be used depending on the prices of gas and electricity. The system can select the type of boiler that has the cheapest energy source at any given time.
  • Parallel heaters can be used to complement the capacity and heat demand of the facility. The combustion thermal fluid boiler could be used as the main heat source during peak demand or when a constant and high heat supply is required. The electric boiler could come into operation during low demand periods or when a quick and precise response to changes in thermal load is needed, or vice versa.
  • The combination of parallel boilers provides greater operational flexibility. For example, when a significant additional heat is needed, both boilers could operate simultaneously to meet the demand.
  • As mentioned earlier, one reason for implementing a hybrid system is to improve the efficiency of the heating system and implement a decarbonization process in the company.
  • Having two types of boilers provides additional backup in case one of the units fails. This improves system reliability and reduces the risk of production interruptions due to technical issues.

It is important to have appropriate control and automation systems to ensure that both boilers can work together efficiently and cohesively. Control systems should adjust the operation of each boiler according to heat demand and other factors.

Smart hybrid system

The R&D department at Pirobloc is developing a smart system that can access a database containing gas and electricity prices to decide which boiler to activate based on the cheapest energy source at any given moment.

This approach offers several potential benefits:

  • Cost optimization: The intelligent system can make informed decisions about which boiler to use based on the current prices of energy sources. This could help reduce operational costs by using the most economical energy source at any given time.
  • Energy efficiency: By choosing the cheapest and most efficient energy source based on current demand, the system could contribute to greater energy efficiency in industrial operations.
  • Flexibility: The system could adapt to fluctuations in gas and electricity prices and demand, allowing for greater flexibility in heat management and production.
  • Decarbonization: If electricity comes from renewable or low-carbon energy sources, the intelligent system could contribute to further decarbonization by prioritizing electricity when it is more sustainable.
  • Automation: The system could operate autonomously, reducing the need for constant human intervention in making decisions about which boiler to activate.
  • Emission reduction: By using the cheapest and potentially cleanest energy source in terms of emissions, the system could help reduce greenhouse gas emissions and other pollutants.


1.- Object of the study

A client has requested a study to assess the replacement of two 1,500,000 kcal/h fuel oil thermal oil boilers with two electric boilers of lower power. The exact power required is to be determined in this study.

The client wishes to change their operating routine from the current 10 hours of daily operation to continuous operation, 24 hours a day. The goal is to prevent the cooling of the stored product (asphalt tar) and have the heaters maintain a stable temperature for the product, compensating for losses to the environment.

The change of fuel, from fuel oil to electricity, is a result of the client’s commitment to reducing emissions in their area of influence.

For this energy transition, the client requests to keep one of the two existing boilers as a backup, but to switch its fuel source from fuel oil to diesel, which is a less polluting option than fuel oil.

2.- Current situation

At the request of shipping companies, the client must maintain 5 tanks of asphalt tar (9,000 tons) at a temperature of 150ºC to facilitate the handling and pumping of the product.

Currently, the 1,500,000 kcal/h (unit power) fuel oil heaters are in operation simultaneously for 10 hours a day, which is the duration of the workday. At the beginning of the workday, the boilers operate at 100% power. Around midday, the power is reduced to the first stage of the burner. At the end of the workday, the client shuts them down until the next morning when this work cycle begins again. It is estimated that the average temperature loss per tank is a maximum of 2ºC per day.

3.- Detected deficiencies

The client’s operating method results in excessive fuel oil consumption. The usual practice in this type of plant is the opposite, as the optimal solution is to maintain the temperature of the stored product constant. This way, they can minimize the required boiler power and the plant’s consumption.

4.- Flow analysis

It is assumed that, to ensure the correct operation of the entire installation, the same flow range must be maintained. This makes all the design of the heating coils and other control elements of the existing thermal oil part of the plant remain valid.

For this reason, the study of the power change starts with the analysis of flows.

The main DN-150 (6″) line can handle a maximum flow rate of around 220 m3/h, with fluid velocity below 3.5 m/s, complying with current regulations in this regard.

Therefore, each of the two electric boilers will be designed to handle a flow rate of 110 m3/h, resulting in a pipe size of DN-125 and a fluid velocity of 2.5 m/s (optimal from the point of view of pressure loss vs heat transfer).

5.- Pressure loss analysis

To determine the actual pressure loss of the installation, we start from the existing fuel oil boiler pumps. To do this, we perform a simulation that estimates the pressure loss based on the nominal flow rate of each pump and the kW of the motors.

After the simulation, we observe that each existing pump can overcome a pressure loss of about 6 bar_g @ 240ºC.

The pressure loss of the electric boilers can be adjusted from a minimum of 1.5 bar_g for proper instrumentation readings. Furthermore, it is estimated that the boilers to be replaced have a pressure loss of about 2.5 bar_g.

Therefore, we will adjust the pressure loss of our electric boilers to 1.5 bar_g, resulting in an equivalent selection for the installation of a pump with a manometric head of 5 bar g.

To select the pump for each recirculation group of each electric boiler, we start with the following data:

  • Flow rate of 110 m3/h
  • Working temperature of the thermal oil: 240ºC
  • Pressure loss: 5 bar_g

After tests and simulations, we obtain a 30 kW motor, which represents a reduction of 7 kW in electrical consumption compared to each currently installed boiler.

Each impulsion pump of each electric boiler will incorporate a variable speed drive for startup and to adapt to the optimal operating point of the current installation.

6.- Required power analysis

To determine the optimal power to install, we will start from the different design scenarios requested by the client and the flow analysis conducted earlier.

Data provided by the client:

Current energy loss working 10 hours with fuel oil boilers: 2ºC/day
Boiler setpoint temperature: 240ºC
Actual thermal jump of the boilers (according to SCADA): 10ºC
The client has requested an analysis of different design scenarios, taking into account that the goal is to maintain the temperature of 5 tanks of asphalt tar (9,000 tons) simultaneously at 150ºC for easy pumping. Additionally, the client indicates that the amount of asphalt tar that needs to be kept at 150ºC more frequently is 5,000 tons.

Calculation of the necessary heat energy for each scenario:

  • 9,000 tons @ dT 1ºC and dT 2ºC
  • 9,000,000 kg · 0.516 kcal/kg·°C · 1°C = 4,644,000 kcal
  • 9,000,000 kg · 0.516 kcal/kg·°C · 2°C = 9,280,000 kcal
  • 5,000 tons @ dT 1ºC and dT 2ºC
  • 5,000,000 kg · 0.516 kcal/kg·°C · 1°C = 2,580,000 kcal
  • 5,000,000 kg · 0.516 kcal/kg·°C · 2°C = 5,160,000 kcal

Calculation of power for each electric thermal oil boiler, taking into account the following parameters:

  • Setpoint temperature: 240°C
  • Flow rate: 110 m3/h
  • Real temperature difference of boilers based on SCADA: 10°C

A unit power of 600 kW (516,000 kcal/h) is obtained, resulting in a total power for both boilers of 1,200 kW (1,032,000 kcal/h).

  • 9,000,000 kg · 0.516 kcal/kg°C · 2°C = 9,280,000 kcal
  • Total power of the set of two electric thermal oil boilers: 1,200 kW (1,032,000 kcal/h)
  • Hours required to achieve this: approximately 9 hours of operation at 100% power.

The most unfavorable scenario calculated involves raising the temperature of all tanks by 2°C simultaneously, as the client has indicated that this has occurred on occasion.

In the case of working in the most common scenario and raising the temperature by 2°C:

  • 5,000,000 kg · 0.516 kcal/kg°C · 2°C = 5,160,000 kcal
  • Total power of the set of two electric thermal oil boilers: 1,200 kW (1,032,000 kcal/h)
  • Hours required to achieve this: approximately 5 hours of operation at 100% power.

7.- Conclusions

It is recommended that the boilers operate 24 hours a day to maintain the temperature of the tanks stable, so that the boilers only need to compensate for the losses generated due to the thermal insulation of the tanks. This way, the average consumption of the installation will decrease significantly.

To achieve this, it is estimated that the ideal configuration is to install 2 electric thermal fluid boilers with a unit power of 600 kW, with a total installed power of 1,200 kW.

The electric thermal oil boilers have a 100% efficiency.

We also recommend keeping one of the two existing 1,744 kW boilers as a backup but changing the fuel from fuel oil to diesel. This ensures the energy transition of the plant and a change in operating procedures. Additionally, the use of highly polluting fuel oil is discontinued.

8.- Power and electrical consumption

As part of the engineering study, a calculation of the power required to operate the two new electric heaters is included, as well as different estimates of the monthly electrical consumption in various scenarios.
In this case, the client needs to contract:

  • 1,860 A of power.
  • Line voltage 3Ph 400 V 50 Hz.
  • Recommended supply for each of the electric boiler cabinets: 4 flexible cables of 1x 300 mm2. A total of 8 cables of 1×300 mm2 for the 2 boilers.

The power required to bring the thermal oil installation up to temperature is also calculated, taking into account the following parameters:

  • Total of 15,000 liters of thermal oil
  • Initial temperature: 20°C
  • Final temperature: 220°C (We estimate that we can lower it to at least this temperature with the new working conditions).
  • Density at 20°C: 773 kg/m3
  • Density at 220°C: 837 kg/m3
  • Average density: 805 kg/m3
  • Specific heat at 20°C: 0.52056 kcal/kg·°K
  • Specific heat at 220°C: 0.60288 kcal/kg·°K
  • Average specific heat: 0.56172 kcal/kg·°K
  • Required power: 15,000 liters · 805 kg/m3

0.56121 kcal/kg°C · 200 = 1,356,554 kcal (1,577 kW). Therefore, the required electrical power will be of this order, 1,577 kWe.

As for consumption scenarios, estimates are calculated for maximum consumption and typical consumption with different hours of daily operation.[/vc_column_text]


1. – Object of the study

The purpose of this study is to evaluate the possibility of installing an electric thermal fluid boiler in parallel with the existing thermal oil boiler, which operates on natural gas. The client wants to be able to work with either boiler depending on the fuel price (electricity or natural gas).

2. – Reference documents

The following documents have been considered for this study:

  • Technical information about the current system.
  • Technical information about the current pumping system.
  • Technical information about the client’s thermal oil.
  • P&ID of the current thermal oil system.
  • Electrical diagrams of the current system.

3. – Description of the current boiler room

The thermal fluid heater room consists of the following main equipment:

  • Thermal fluid boiler that operates on natural gas and has a heating capacity of 698 kW (600,000 kcal/h).
  • Main group of DN-80 PN-16 recirculation pumps. Double execution. Flow rate: 34 m3/h. Motor power: 7.5 kW.
  • Thermal fluid expansion tank with a capacity of 500 liters.
  • Air separator.
  • Thermal fluid collector tank with a capacity of 3,000 liters.
  • Reversible pump group for emptying and filling the installation. Motor power: 0.55 kW.
    Main control panel with regulators. 3Ph 400V 50Hz + N.

4. – Technical solution proposed by Pirobloc

4.1 – Heating capacity

To ensure perfect operation, a boiler with the same capacity as the existing one is proposed. Heating capacity: 700 kW (602,000 kcal/h).

The thermal fluid boiler must be able to meet the same heating ramp constraints as the existing boiler. We ensure that the system’s startup times will be the same after a technical shutdown.
We conducted simulations with both boilers to ensure that the results obtained are as expected by the client.

4.2 – Selection of the thermal fluid pump

To ensure the proper operation of the entire installation, the existing flow rate range must be maintained. This way, the design of the heating and thermal installation control elements will remain valid.

The pump in the existing system has the following characteristics:

  • TDC 50-200
  • 7.5 kW
  • 3Ph
  • 400V
  • 50 Hz.
  • Flow rate: 34 m3/h

The size of the main DN-80 PN-16 recirculation pump group is valid for 40 m3/h.

We recommend increasing the flow rate of the new electric thermal fluid heater to 40 m3/h to facilitate heat exchange and optimize the system’s hydraulics.

The DN-80 pipe with a thermal fluid velocity of 2.33 m/s is valid for 40 m3/h.

We select the following pump NTT 50-200 11 kW. 3Ph 400V 50 Hz.

Before selecting the new pump, we conducted simulations at 215°C (working temperature) and 40°C (cold start).

4.3 – Calculation of the total volume of thermal fluid for the new electrical system

The existing thermal fluid collector tank has a capacity of 3,000 liters and is valid for the new system.

4.4 – Calculation of the new expasion tank for the new heating system

The existing thermal fluid expansion tank, which has a capacity of 500 liters, is not valid for the new system.
We propose a thermal fluid expansion tank of 1,000 liters.

4.5 – Calculation of the electrical power needed for the new hot oil heater

  • Electric thermal fluid boiler CE-700 700 kWe
  • Main recirculation pump group 23 kWe
  • Control 2 kWe

Total kWe 725 kWe

Total A 1,163 A (3Ph 400V 50Hz)

As for cables, the following are suggested:

  • 3x Cables per phase of 240 mm2
  • A total of 9 cables of 240 mm2

5. – Proposed boiler room

The following equipment will be added to the boiler room:

  • An electric thermal fluid boiler from the PIROBLOC brand. Model CE-700. Heating capacity 700 kW (602,000 kcal/h).
  • Main group of DN-80 PN-16 recirculation pumps. Double execution. Flow 40 m3/h. Motor power 11 kW.
  • New vertical and cylindrical thermal fluid expansion tank. Capacity 1,000 liters. To replace the existing 500-liter tank.
  • Main control panel with PLC. 3Ph 400V 50Hz + N.
  • Boiler selector panel.

A P&ID with the proposed heating room will be provided to the client.

The engineering report also includes the following:

  • New dimensions of the boiler room.
  • Boiler room controls: through a boiler selector panel, we can choose which boiler to work with at a given time. This will be located outside the heating room between the control panel of the old boiler and the new PIROBLOC boiler control panel.
  • Modifications to the current boiler room.
  • Connection points: thermal fluid inlet and outlet connections; modifications to the current collector tank, including connections to the safety valve of the electric thermal fluid boiler and the drain line of the CE-700; connections to the new expansion tank; connections to the main control panel, which will be located outside the boiler room between the control panel of the old boiler and the new PIROBLOC control panel.