Reducing the Cost of Steam Generation
Fuel price volatility, particularly the recent doubling of solid fuel prices like coal, has drastically increased the cost of steam generation, eliminating the former cost advantage of solid fuels.
The cost of steam generation can be mathematically reduced by two key variables: increasing feed water temperature (hg-hf) and increasing direct boiler efficiency (η).
Implement heat recovery strategies, including recovering condensate and flash steam, and recovering heat from blowdown and flue gas streams.
Optimise the air-to-fuel ratio, maintain precise draft pressure, achieve the ideal bed temperature, and ensure proper insulation.
Steam is a critical utility in process industries, and its generation cost directly impacts OpEx and product costs. Energy demand is rising, and while solid fuels like coal meet a large portion of this demand, recent fuel price spikes have tripled the cost of coal-generated steam compared to ten years ago, eliminating the former cost advantage over gas or oil. Implementing actions to reduce steam generation costs not only mitigates the effects of current price shocks but also provides long-term benefits as fuel costs continue to increase annually.
To generate the same amount of steam for less, the focus must be on optimising the two variables defined by the cost formula:
Cost of Steam Formula
Cost of steam = (hg-hf) x cost of fuel / GCV x η
Where:
- (hg-hf): Represents the total heat supplied (enthalpy of steam minus enthalpy of feed water). Increasing the feed water temperature (hf) reduces the required heat input and consequently lowers the fuel needed to generate steam, resulting in a lower cost per unit of steam.
- η (Eta): Denotes the direct efficiency of the boiler. As boiler efficiency increases, the overall cost of steam decreases.
How to Reduce Heat Demand by Improving Feedwater Temperature?
Increasing feed water temperature is achieved through effective heat recovery. This process reduces the quantum of heat required from the fuel, directly lowering the cost per unit of steam. Key actions to improve feedwater temperature include:
- Recovering every drop of recoverable condensate (aiming for >95% of indirect steam consumption).
- Recovering flash steam.
- Recovering heat from other streams, such as blowdown flash recovery, blowdown water heat recovery, and flue gas heat recovery.
What are the Best Practices for Improving Boiler Efficiency?
Boiler efficiency is determined by how effectively the energy in the fuel is transferred to the steam. Improving boiler efficiency (η) is crucial for reducing the overall cost of steam generation. This can be ensured by focusing on operational optimisation:
- Maintaining the optimum air-to-fuel ratio.
- Ensuring precise draft pressure.
- Achieving the ideal bed temperature.
- Operating the boiler efficiently at its rated pressure.
- Implementing proper insulation.
In conclusion, effectively managing the cost of steam generation is no longer just about fuel choice, but about operational excellence. By systematically implementing strategies for heat recovery like maximising condensate and flash steam recovery and relentlessly pursuing boiler efficiency through optimisation of air-to-fuel ratio and insulation, industrial facilities can significantly mitigate the impact of fluctuating fuel prices. These measures not only reduce OpEx but also contribute to a more sustainable and resilient operation. Taking action today is critical to securing a competitive cost advantage in the long term.
