Expert Solutions for Boiler Ash Fouling and Slagging

The Challenge of Ash Fouling

Boiler ash fouling and furnace slagging are unavoidable consequences of combustion, particularly when firing biomass, waste-derived fuels, or lower-grade coals. As fuel quality becomes more variable, ash chemistry becomes increasingly difficult to manage.

Over time, deposits accumulate on heat transfer surfaces, creating a triple threat to plant performance:

Reduced heat transfer and falling thermal efficiency
Rising flue gas temperatures that increase stress on downstream equipment
Unscheduled and lengthy outages for manual cleaning and maintenance

Many plants still rely on reactive “shovelling and blasting” approaches once performance has already declined. This creates unnecessary downtime, higher operating costs, and lost generation.

The goal is clear, move from reactive cleaning to proactive online boiler cleaning that minimises and controls ash deposits before they become a problem.

Request a Plant Performance Audit

Understanding Ash Deposits

Effective ash deposit removal begins with understanding how and where deposits form.

Fouling vs. Slagging – Identifying the Threat

While both of these problems result in unwanted deposits, they occur in different parts of the boiler and present unique physical challenges. Understanding these distinctions is critical for implementing an effective removal strategy.

Convective Fouling

Fouling mostly occurs in the convective passes and heat recovery sections (such as superheaters, reheaters, and economisers).

The Process: Fine, fly-ash particles are carried by flue gases and adhere to relatively cooler tube surfaces.
The Impact: Over time, these particles sinter into insulating layers that significantly restrict gas flow and reduce thermal efficiency.
The Challenge: In modern biomass and EfW plants, these deposits often contain high levels of alkali metals and chlorides, making them stickier and more resistant to traditional compressed air or acoustic cleaning.

Furnace Slagging

Slagging is a higher-temperature phenomenon found in the furnace and radiant sections, where ash is in a molten or semi-molten state.

The Process: Molten ash particles strike the furnace walls or leading tube banks, cooling rapidly and bonding to the metal.
The Impact: This forms dense, glass-like “clinkers” or hard sheets of slag. Large slag falls can cause catastrophic mechanical damage to the lower boiler components and grate systems.
The Challenge: Slag is notoriously difficult to remove online. Once it bonds to the radiant surfaces, it acts as a powerful thermal insulator, forcing the boiler to work harder and driving up flue gas exit temperatures (FGET).

The Cumulative Effect

Left unmanaged, both fouling and slagging create a “downward spiral” of performance. As heat transfer is restricted, the boiler must increase fuel throughput to maintain steam conditions, which in turn raises furnace temperatures, accelerating further deposit formation and increasing the risk of accelerated tube corrosion and material degradation.

In addition, unplanned outages become more frequent and of longer duration in order to remove the large build-ups of fouling and slagging material.

The Role of Fuel Variability

Modern boilers increasingly operate on blended fuels, including biomass, refuse-derived fuel, and waste wood. These fuels often contain high alkali and chlorine levels, resulting in lower ash fusion temperatures.

As a result, deposits form more quickly, bond more tightly, and become harder to remove using conventional methods. Biomass boiler fouling, in particular, presents significant challenges for long-term reliability.

Why Conventional Cleaning Often Fails

Many plants rely on traditional sootblowing systems and supplementary cleaning tools. While these methods have a role, they often fail to control modern ash fouling effectively.

Steam Sootblowers

Steam sootblowers are limited by several inherent drawbacks:

Erosive damage to boiler tubes over time
Line-of-sight restrictions that leave shadowed areas untouched
High operational cost from diverting valuable plant steam

These issues reduce equipment life while failing to deliver consistent ash deposit removal.

Acoustic Horns

Acoustic horns can dislodge loose, powdery ash but have limited impact on dense, sintered, or bonded deposits. Their effectiveness decreases significantly as fouling severity increases.

The RJM Difference

RJM addresses these challenges directly by providing a sootblower alternative designed for modern fuel environments and continuous online operation.

The RJM IMPULSE® Cleaning System

RJM’s IMPULSE® Cleaning system uses advanced, supersonic pulse detonation technology to deliver high-energy cleaning without mechanical contact.

How It Works

IMPULSE® Cleaning generates controlled detonations that produce a supersonic shock wave. This shock wave propagates through the boiler gas path, breaking the bond between ash deposits and heat transfer surfaces.

Rather than relying on directed jets, the system uses pressure dynamics to clean large volumes effectively.

Non Line-of-Sight Cleaning

Unlike traditional sootblowers, the shock wave wraps around tube banks and penetrates complex geometries. This enables effective cleaning in areas that mechanical systems cannot reach.

Shadowed surfaces, tight tube pitches, and congested heat exchangers are cleaned consistently and uniformly.

Key Benefits

No Tube Erosion
No mechanical contact means no wear on heat transfer surfaces.
Increased Availability
Proven to deliver up to a 5% increase in plant availability, as demonstrated at Ince Bio Power.
Zero Steam Usage
Preserves exported power and improves Net Heat Rate by eliminating steam consumption.
Small Footprint
Compact installation allows easy retrofitting to existing boiler walls and penthouses.

These benefits combine to deliver cost-effective, reliable, long-term online boiler cleaning and improved operational stability.

Find Out How IMPULSE® Technology Works

Applications & Fuel Types

RJM systems are deployed across a wide range of combustion environments.

Waste-to-Energy (EfW)

EfW plants face highly complex and corrosive ash compositions. IMPULSE® controls deposit build-up while protecting tube materials and maintaining heat recovery performance.

Biomass & Wood Waste

High-alkali biomass fuels accelerate fouling and slagging. RJM solutions stabilise performance and reduce the impact of biomass boiler fouling.

Utility Coal

Ageing coal-fired assets benefit from improved thermal efficiency, lower maintenance costs, and extended operating life.

Industrial & Co-generation

For industrial boilers and CHP plants, consistent ash deposit removal maximises uptime and protects critical production processes.

Case Study – Ince Bio Power

RJM’s IMPULSE® system has delivered measurable performance improvements at Ince Bio Power.

Following installation, the plant achieved:

Improved boiler cleanliness
Stabilised heat transfer
Reduced unplanned outages

This resulted in 19 additional days of generation per annum, directly improving revenue and operational resilience.

Find out More

Specialist Consultation and Engineering Support

RJM provides more than hardware. Our approach is built around combustion analysis, operational data, and plant-specific engineering.

We support clients through:

On-site surveys and performance assessments
CFD modelling of gas flow and deposit formation
Optimised placement of IMPULSE® Cleaning units
Ongoing technical support and optimisation

This combustion-led methodology ensures that each ash fouling solution is tailored to the unique characteristics of your boiler.

Ready to Eliminate Boiler Fouling?

If you are experiencing reduced thermal efficiency, rising maintenance costs, or persistent furnace slagging, RJM can help.

Speak to our combustion engineering specialists to discuss your plant’s requirements and explore the most effective ash deposit removal strategy.

Talk to an Expert
Winchester Office: +44 (0)1962 831 250

Get in Touch

Optimise Performance with IMPULSE® Cleaning

IMPULSE® Technology Versus Traditional Shock Pulse Cleaning

Evaluate the operational advantages of IMPULSE® over high-maintenance shock pulse systems. This comparison highlights how our pulse-combustion technology delivers more consistent cleaning performance with significantly lower operating costs and reduced mechanical wear on your plant.

IMPULSE® vs Shock Pulse Cleaning

Advanced Solutions for Boiler Ash Fouling and Slagging

Address the root causes of slagging and fouling with RJM’s bespoke engineering. From combustion audits to IMPULSE® cleaning, we provide integrated solutions that extend generation campaigns, maximise MWe output, and reduce the need for manual cleaning interventions.

Boiler Ash Fouling and Slagging

Comparing IMPULSE® Cleaning with Traditional Soot Blowers

Discover why IMPULSE® technology offers a superior, non-erosive alternative to steam soot blowers. Learn how to eliminate tube erosion, reduce steam consumption, and improve cleaning coverage across all heat transfer surfaces for enhanced boiler reliability.

IMPULSE® vs Soot Blowers

IMPULSE Cleaning® System

The IMPULSE® Cleaning System is a development of the pulse detonation propulsion technology pioneered by GE and uses a supersonic shock wave, created by the detonation of a mixture of fuel and air, to dislodge material that has built up on surfaces within the boiler.

IMPULSE Cleaning System

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Customer Reviews

I would like to thank RJM for its support in 2020 which helped us successfully pass the 95% installed capacity test. This enabled Energy Works Hull to qualify for the Contract for Difference subsidy scheme. I believe RJM was instrumental in the screw design, screw speed and fuel feed operation to help us achieve this. I also think the RJM approach of great ideas, designing, modelling and implementing has helped us with this success.

Mark Roberts Head of Engineering, Evero

A very professional service that exceeded expectations. They really enjoyed doing the engineering – you can tell that from the way they worked. I would highly recommend RJM International for any combustion engineering.

Bruse Toase Head of Engineering, Indivus Limited

The team at RJM brought great experience, data analytics and modeling to help us solve our challenging combustion issues at our 1200 MW station in Vietnam. It was a pleasure working with a team which was as determined and dedicated as we were to find the solutions.

Kevin Pierce Plant Manager, AES-VCM Mong Duong II, Vietnam

This plant is now operating better than ever before.

Ömer Buğer CEO, Eren Enerji

SG6 has been running all week at 12-13MW with no issues and I just wanted to say thanks so much for the work on this – it’s a phenomenal improvement.

John Lynch Energy and Oil Movements Processing Manager, Irving Oil, Whitegate Refinery

We operate an incinerator for hazardous industrial waste. Our fuel composition is poorly specified and varies hour by hour. Despite this, the team from RJM took great interest in our plant and produced a very helpful assessment of NOx emissions based upon an analysis of our operational data and a pragmatic review of the equipment involved.

Ian Richards Senior Process Engineer, Tradebe

RJM have made a valuable contribution in the development of the Uskmouth Conversion Project. I have been particularly impressed by RJM’s ability to simplify the technically-complex risks associated with the development of a new fuel and combustion system to critical commercial drivers for Board briefings. RJM have some great people who are without doubt world-leading in their sphere of expertise.

Ernie Rowe Head of Conversion, SIMEC Atlantis Energy

RJM have worked co-operatively with us in proceeding towards the goal of full conversion of Uskmouth Power Station; bringing a flexible approach to this first-of-a-kind project, including taking on works outside their normal realm to ensure the development progressed.

Sophie Murr Head of Project Controls, Uskmouth Power Station

This was a very critical project, being both technically challenging and operating to a tight schedule. The results have enabled the plant to generate reliably while meeting the latest emissions targets.

Peter Lithgow AES Country Manager, Bulgaria

RJM played a key role in the delivery of the Uskmouth Conversion FEED project. RJM’s technical capability in solid fuels, combustion and CFD modelling was essential to the successful outcome of the project and WSP is proud to have had RJM as part of the project team.

Mike Hewson Project Manager WSP (Uskmouth Conversion Project)

RJM International provided an excellent Biomass Conversion Project Scoping Study in 2015 that far exceeded our expectations. It included a number of innovative and cost-effective options for which we are currently seeking approval to proceed. And unlike those studies received previously from others, RJM’s very comprehensive study did not cost a fortune.

James Busche Chief Executive Officer, SIMEC Uskmouth Power

The performance is outstanding and following our comprehensive cost analysis per tonne of NOx reduction, the RJM solution is by far the lowest cost option we could have chosen to meet IED compliance. The lower our NOx, the greater number of hours we can generate, so we are thrilled with the performance of RJM’s Ultra-Low NOx burners. The project was completed on time and within budget.

Neil Cranswick Station Manager, Rugeley Power Station, UK

We will definitely consider to use RJM in future projects.

Olivier Marquette CEO, AES Bulgaria

The team praised the professional manner in which each obstacle was overcome by RJM and the planning and execution of all the activities during the installation and commissioning of the new RJM burner. Overall, we consider RJM’s activity to have been ‘excellent’ and I would like to thank all of you at RJM for your commitment to this project.

Peter Bell Whitegate Refinery, RWE Generation UK

This was a very challenging project technically and in terms of schedule but the results have exceeded expectations, with emissions well below the required limits. We will definitely use RJM in future projects.

Lyle Woodard Director of Construction Global Engineering and Construction Group, AES Corporation, USA

RJM is definitely a great company to work with. The work RJM did here was also very good value for money, so we are completely satisfied.

Jos Peeters Senior Asset Engineer, Essent Energie, the Netherlands

We are very satisfied with RJM and we would definitely recommend the company to other plants as experienced providers of low NOx expertise and an organisation that can solve any low NOx or combustion problem.

Peter Kiss Engineering Leader, AES Tisza, Hungary

The twenty week planned outage went very smoothly and the burner project was well organised with staged deliveries of burner components. All components were installed safely, efficiently and within budget, and thanks to the full CFD survey, commissioning and optimisation was completed in just four days, with the full burner retrofit firing at full load right from Day 1.

Guy Sharp Technical Support Engineer, SSE Ferrybridge, UK

Thanks to the ADA balancing programme carried out by RJM International, we have been able to improve our burner flame profiles and achieve a level of consistency which meet all our reliability, flexibility and emissions criteria, even at this new reduced load level of 135MWe, down from 155MWe.

Ing. Tonino Maglio Plant Manager, Edipower Brindisi, Italy

RJM accomplished an exhaustive assessment of our boiler firing system operations and its report gave Edipower a comprehensive overview of San Filippo’s boiler performance, clear indications on possible hardware upgrades that could be implemented to reduce emission levels and their individual expected contribution to the overall benefit together with a budgetary estimation of their relevant investment.

Alessandro Sacconi Mechanical Engineering Co-Ordinator, Edipower, San Filippo, Italy