Key points
TL;DR:
Upgrading valve actuators and positioners can significantly improve combustion efficiency in waste-to-energy plants. By optimising airflow during combustion and reducing compressed air use operators can cut emissions reduce mechanical stress and improve energy efficiency.
Modern digital positioners like ABB’s TZIDC and EDP300 offer precise control lower air consumption and improved reliability. These upgrades can save up to £1,200 per unit annually in energy costs making them one of the most effective steps toward sustainable and cost-efficient waste energy production.
ABB’s Jo Kirkbride, Product Manager Actuators and Positioners and Force Measurement for ABB Measurement & Analytics UK and Ireland explains how upgrading valve actuators and positioners can help waste energy producers to improve fuel combustion efficiency, reduce compressed air consumption, increase sustainability and achieve more efficient plant operations.
The production of electrical power from the incineration of combustible waste is an increasingly important part of the European energy generation landscape. Electricity generation by waste energy producers – also known as Energy Recovery Facilities (ERF) – already represents just over 3% of the UK’s total power output[i], with the overall contribution of waste to production from non-fossil fuel sources predicted to grow steadily over the next few years.
In common with other industries, ERFs are under commercial and regulatory pressures to maximise plant performance while optimising the overall energy efficiency and sustainability of their operations.
The combustion of any kind of fuel source in air itself produces CO2 and other emissions. In the case of waste energy facilities, however, the impact of these carbon emission is offset by the fact that fossil fuels – oil, gas and coal – are no longer being burned to achieve this.
Electricity generation by waste energy producers – also known as Energy Recovery Facilities (ERF) – already represents just over 3% of the UK’s total power output
Around 90% of the electrical energy consumed by a compressor ends up as waste heat
Controlling combustion
Optimising the efficiency of waste incineration demands accurate control of air flow during combustion to account for factors such as variations in fuel quality, as well as correspondingly precise control of superheated steam and water flow rates and pressure in boilers and condensers.
Here valve actuators and positioners play a critical role in maintaining precise and continuous positioning of the final control elements used to control flows of air and other variables that impact on combustion performance.
Achieving optimum combustion efficiency means supplying the correct amount of air needed to completely combust the waste that’s being used as fuel, while reducing unwanted by-products such as excess CO2, NOx and other atmospheric pollutants that are caused by poor combustion control. Finding this combustion ‘sweet spot’ demands extremely fine control of the amount of air being supplied to the combustion process.
Introducing too little air results in incomplete combustion and inefficient use of fuel. Similarly, too much air increases generation of pollutants that must be removed through the costly purification of exhaust gases. Where excess air is applied to help improve the mix, there’s also the added issue of mechanical stress on the fresh air damper system as supply is continuously throttled to achieve the required level.
In these conditions, valve positioners play a critical role in helping to maintain the ideal mix of fuel and air – and at the right pressure – to optimise combustion while minimising exhaust gas emissions.
A further example of the use of valve positioners in waste energy plants is controlling the injection valves that are used for adding cooling water to reduce the temperature of superheated steam before it’s introduced into the turbine.
This ensures that steam temperature is maintained within a specified range, optimising turbine efficiency and avoiding the risk of damaging components. Poorly specified or operated actuators for injection valve control can compromise the levels of precise control needed for efficient turbine operation.
The force required to open and close control valves is provided by actuators that may be operated either electrically or pneumatically. A complementary role is played by valve positioners that continuously monitor the process variable – such as flow rate – responding with reactive adjustments from a plant or process control system to ensure that the correct valve position is maintained.
Essential air supply
Operation of the numerous pneumatic valve actuators and positioners found in a modern waste energy recovery facility depends on a reliable supply of compressed air that is typically produced on site. Far from being a ‘free’ resource, compressed air is extremely expensive in energy terms. With compressed air being widely used in many industrial processes, its generation is estimated to account for around 10% of industrial electricity consumption.
Air compressors are intrinsically inefficient devices from a thermodynamic point of view. Around 90% of the electrical energy consumed by a compressor ends up as waste heat, leaving just 8%-10% of electricity being converted into usable energy as compressed air to operate control valves and other equipment.
Every control valve positioner consumes compressed air, even when it is motionless in a steady state. Positioners from different manufacturers have widely varying consumption rates. From a waste energy provider’s perspective, therefore, it is clearly desirable to fit positioners with the lowest possible steady state air consumption – or to replace older, less efficient models with newer designs wherever possible.
But how much are these savings worth in practice? Let’s take as an example the typical application of a valve positioner being used to regulate airflow during combustion. As a rough estimation let’s assume that the positioner spends 50 percent of its operational time in a steady state position.
Assuming a compressed air cost of 1p per scfm (standard cubic feet per minute), the cost of this wasted energy could exceed £2,000 per positioner every year. Replacing these positioners with electronically configurable digital positioners such as ABB’s TZIDC or EDP300 could save between £500 and £1,200 annually per positioner – a cost improvement of up to 60%.
Reducing losses, optimising efficiency
As well as optimising the efficiency of fuel combustion, upgrading to latest-generation valve positioner and actuator technology can significantly reduce the cost of air lost to inefficient positioners. Indeed, this represents one of the most important single energy saving actions that waste energy producers and other industrial facilities can take.
Waste energy facilities can realise several benefits by upgrading their legacy actuators and positioners to newer, more efficient components. As well as offering best-in-class positioning performance, latest-generation components enable greater cost savings for plant operators through lower valve positioner air consumption, coupled with greater reliability, longer operating life and reduced maintenance needs.
Upgrade and save with ABB
Long-term savings in energy consumption must be considered in the context of capital costs for upgrading existing components. The potential savings for waste energy operators afforded by upgrading to latest components can be estimated using ABB’s online positioner compressed air cost calculator.
The tool highlights the annual energy savings that can be achieved by upgrading to ABB EDP300 and TZIDC digital positioners. Offering class-leading positioning accuracy and best-of-breed steady state air consumption performance, their rugged design also offers high immunity to environmental factors including temperature, humidity and vibration that are typically experienced in energy generation environments.
FAQs
Why are valve actuators and positioners important in waste-to-energy plants
They control airflow and steam in combustion and turbine systems to optimise efficiency and reduce emissions.
What happens if airflow is poorly controlled during combustion
It leads to incomplete combustion higher emissions and mechanical stress on air supply systems.
How do positioners help improve combustion efficiency
They maintain the ideal air-to-fuel mix ensuring complete combustion and stable turbine performance.
Why is compressed air a concern for energy efficiency
Compressed air generation is energy intensive with only 8%-10% of energy converted into usable power.
How much compressed air do positioners typically waste
Older positioners can waste thousands of pounds worth of air annually even when idle.
What savings are possible with modern digital positioners
Upgrading to ABB’s TZIDC or EDP300 can save between £500 and £1,200 per unit per year.
How can plants calculate their potential savings
ABB offers an online cost calculator to estimate compressed air savings from upgrading positioners.
What additional benefits do modern actuators and positioners offer
They improve reliability extend lifespan and reduce maintenance costs especially in harsh conditions.
Why is this relevant to sustainability goals
By reducing compressed air use and improving combustion control plants lower CO2 output and energy waste.
Are these upgrades difficult or expensive to implement
The capital cost is offset by annual energy savings and long-term performance improvements.
