Reducing Fuel Consumption by £213,000 per Annum: Recovering Waste Heat at a Large-Scale Snack Manufacturing Facility
Operational Context
A specific manufacturing facility in northern England operates large-scale industrial heating systems dedicated to high-volume snack production. The production process relies on a 12MW heater system, which generates significant volumes of flue gas. During standard operation, these gases were exhausted at temperatures of 185°C, representing a substantial loss of process heat that was vented directly into the atmosphere.
The facility management engaged EnerTherm Engineering to address this thermodynamic inefficiency. Following an initial site audit, the engineering team utilised the energy recovery proposal document to assess the feasibility of capturing this waste energy. The primary objective was to improve overall thermal efficiency by integrating a heat recovery system to preheat the combustion air entering the heater units, thereby reducing the fuel consumption required to maintain process temperatures.
Engineering Methodology and Design
The project began with a rigorous data capture and analysis programme. EnerTherm Engineering utilised Pinch Analysis to identify the optimal integration points for heat recovery. This approach ensures that the design maximises the temperature difference between the recovered heat and the process demand without causing process instability.
The team analysed the flue gas composition and temperature profiles across the operational cycles. Because the facility produces snack products, the flue gases were rich in thermal energy but required careful management to prevent fouling of the heat exchanger surfaces. The design phase involved the following steps:
- Detailed site survey and flow rate analysis.
- Scenario building to model the impact of varying throughput on heat recovery potential.
- Development of Process & Instrumentation Diagrams (P&ID) and Process Flow Diagrams (PFD).
- Selection of appropriate material specifications for the economiser unit to ensure longevity in a high-temperature environment.
Technical Implementation
The final design specified a system capable of recovering 500kW of energy from the flue gas stream. The core of the solution involved directing the waste heat to preheat the combustion air, which was raised from an ambient intake temperature of 20°C to 130°C prior to entering the burners.
This CFD-modelled approach ensured that the combustion process remained stable despite the higher inlet air temperature. EnerTherm Engineering managed the project delivery, which followed a defined timeline:
- Design Phase: 3 weeks.
- Equipment Build and Procurement: 16 weeks.
- On-site Installation: 2 days.
The installation was carefully scheduled to minimise disruption to the facility's production cycle. By leveraging prefabricated modules, the onsite installation time was kept to a minimum, ensuring that the facility returned to full production capacity immediately following the commissioning phase.
Quantifiable Operational Gains
Post-installation monitoring confirmed that the combustion air preheating system achieved the calculated energy savings. By preheating the intake air, the heater burners required significantly less gas to reach the target operating temperatures. The system provided a consistent reduction in fuel consumption, with savings of 3 to 4 per cent, depending on daily throughput.
Financial performance and energy metrics were tracked over a three-week period immediately following the commissioning of the equipment. The following table illustrates the comparative annual savings across two distinct production lines at the facility:
| Metric | Line One | Line Two |
|---|---|---|
| Gas Saving per Annum (m³) | 19 m³/h | 22 m³/h |
| Energy Saving (kW) | 210 kW | 243 kW |
| Total Energy Save per Annum (kWh) | 1,677,504 kWh | 1,942,373 kWh |
| Annual Gas Cost Savings | £184,525 | £213,661 |
| Total Capital Investment | £431,000 | £603,400 |
| Project Payback Period | 2.3 Years | 2.8 Years |
"The successful integration of this heat recovery system demonstrates that recovering energy from high-temperature flue gas is one of the most effective ways to lower operational costs in food manufacturing. By raising the combustion air temperature from 20°C to 130°C, we not only improved fuel efficiency but also delivered a project with a sub-three-year return on investment." - Project Lead, EnerTherm Engineering.
This case demonstrates the efficacy of targeted thermal engineering in industrial environments. By treating flue gas as a valuable energy resource rather than a waste byproduct, the facility has successfully reduced its annual fuel expenditure by over £213,000 on its highest-output line, while simultaneously reducing the carbon footprint associated with its heating operations.
Managing Director — EnerTherm Engineering
Dr. François Pierrel is Managing Director of EnerTherm Engineering with over two decades of expertise in thermal design, heat transfer, and industrial energy optimisation. He holds a PhD in Heat Transfer from Cranfield University and a Post-Doctorate from Heriot-Watt University.
