About the author
Roberto Vogel is the founder and director of Vogel Waste Industry Services trading as of ENPRO SWISS, former chief commissioning engineer for Von Roll Inova (now HZI), founder and technical director of KRR ProStream (now retired) and EWB editorial panel member
1. Introduction
Training and competence of people at the coalface of modern energy-from-waste plants is crucial for safe and sustainable operations of these valuable assets. If done well it has the potential of saving on operational and capital cost, as well as avoiding potential reputational damage through preventing things from going wrong.
In his career as a commissioning engineer (which has included training of plant operators), consultant and provider of services to this industry, I have experienced the training and competence (T&C) aspect from various perspectives. This article is a summary of this experience and contains his conclusions based on practical examples, as well as important learning points and recommendations.
Those operating the best EfW plants find training is important for a number of reasons, including:
The very varied nature of the feedstock and rogue elements contained within
Strong emphasis on environmental legislation and compliance
The need for high availability, given the public health element of EfW (90% plus)
The large variety of different processes (chemical, physical, logistic)
The relatively rapid and ongoing growth of modern EfW in the UK, leading to pressure on personnel recruitment and training.
2. What is the challenge?
Lack of process understanding, and incompetence carry the risk of process failure, loss of production and other unplanned/unbudgeted costs. But operating and maintenance staff with a good understanding of the process they manage, and high competence in their disciplines, results in high quality operations, better profitability and better environmental performance.
Operation and maintenance staff with good T&C in their respective disciplines measurably improve plant availability, minimising the impact of waste going to landfill and increasing profitability for the companies running these facilities.
In the following the author will present six recent real life mini case studies, illustrating the importance of process awareness and competence. If you are involved in the practical day-to-day running of EfW plants, you may recognise similar events as these are more frequent than most of us like.
3. Case studies
Case one: Failed rapping system
The first example concerns the breakdown of a rapping system on the horizontal boiler pass. This failure was not originally seen as a high priority by the operating team. This quickly changed as the gas path in the horizontal pass of the boiler got blocked to such a degree that the induced draft (ID) fan couldn’t cope, resulting in positive flue gas pressure inside the boiler. In turn this led to smoke emissions into the boiler hall. By this time it was too late to take any mitigating action; the plant was taken off-line at an average cost (in the UK) of £50,000 a day for an unplanned stoppage.
In this case, not giving the rapper failure a high priority cost the operator £250,000 for loss of production only, with further costs for offline cleaning.
Good plant knowledge, as part of the training package, would have allowed early detection of the issue and a competent management team would have immediately initiated remedial action. Measures include the reporting and communication of boiler KPIs, giving early warning of the developing issue. This could have led to the deployment of detonation on-line cleaning as a possible mitigating measure.
Case two: Blockage of feed system
A recurring issue in this industry is the blocking of feed hoppers, chutes, or feed tables through oversized waste. Most modern plants are designed so that the operators have a direct view from the control room onto the waste bunker and feed hoppers.
In this case large sections of tree trunks have been “smuggled” into the plant by rogue waste suppliers, as the type and size of compliant waste is clearly specified in the conditions for waste acceptance.
These large pieces of timber got stuck on the feeder table and blocked the feed system. Similarly to case one the plant needed to be taken off-line to remove the rogue elements manually. Again, purely the cost of unplanned shutdown amounted to £250,000, to which labour cost for removal must be added.
General and universal understanding of the waste allowed in the plant might have led to the detection of the large tree trunk sections on their way from tipping to being deposited in the feed hopper.
However, it is noted that it is possible that such rogue elements evade direct detection by control room operators, as some crane grabs are large enough to conceal them. Automatic crane systems take the vigilance of the crane operator out of the equation.
However, awareness regarding the risk of rogue elements at the waste acceptance level could open the way to improved quality control through information campaigns with waste suppliers, spot checks and the threat of large fines as a last resort. Some plants have CCTV systems at vehicle drop-off, which can be replayed if non-conforming waste is detected.
In this scenario T&C at all levels and in different departments have the potential of reducing the risk of financial losses and impaired availability.
Case three: Blocking of riddlings (under-grate ash) chute
The third case concerns the blocking of an under-grate riddlings chute. This can happen in the best-run plants, depending, among others, on non-metal content in the feedstock. For this reason, most modern plants have temperature sensors in riddling and other ash chutes; if the temperature in the chute falls below the alarm threshold, this may indicate no ash is falling through, so a blockage may have occurred. In this event the low temperature alarm was ignored for a long time, in fact enough time for under-grate ash to fill up the under-grate hopper, rendering that grate element inoperable, through blocking the Primary Air (PA) inlet and mechanical operations of the grate’s movement.
The resulting losses were £250,000 plus cleaning and repair costs.
In this case the operators were logging the temperature changes but weren’t trained in the interpretation of the results of their findings, rendering them unaware of the pending failure.
However, well-trained, competent operators would have foreseen the consequences of this course of action, especially when the alarm persisted over many shifts.
Case four: FGT walking floor misdiagnosis
The fourth case study is the failure of the FGT walking floor hydraulic RAM mount. The issue was mis-diagnosed as a reactor blockage when the walking floor failed to meet its limits. The plant was subsequently and prematurely brought offline for offline cleaning. Upon inspection, no blockage was found and further fault finding was conducted. It was then found that the mounting beam for the hydraulic RAM had failed, preventing the RAM making its limit. The repair that was carried out could have been done when the plant was online with no loss in availability.
Well-trained operations and maintenance staff armed with methodical fault diagnostics skills would have identified the failure and engaged in a less costly course of action.
Preliminary analysis of operator staff case studies
The four case studies presented above are from the perspective of the operators of an EfW plants, where lack of T&C has led to worse plant failure, unplanned downtime and potentially waste redirected to landfill.
The lack of training, however, is not limited to EfW plant operators. Contractors that design, build and commission and those that service EfW plants can also impact on the quality of operations through lack of T&C, potentially leading to loss of availability and other unplanned costs. The next two examples are included to show that improved training and competence also helps these stakeholders in the EfW value chain to deliver high quality service for EfW operators and improve their own profitability.
Case five: Primary Air (PA) faults commissioning
The PA pre-heating system is crucial in EfW plants to have a stable, consistent combustion over a wide range of caloric values. In this fifth case study, the PA system was the cause of poor combustion, insufficient feedstock capacity and poor Incinerator Bottom Ash (IBA) quality. However, it took years to identify and rectify the problem.
These issues went on from commissioning to 2019, when the operator discovered that a combination of valve position feedback and temperature sensor position caused the PA to be too cold for the low calorific value of the actual waste. This resulted in the contractor being penalised for not achieving guaranteed performance. Put simply, the two separate construction and commissioning failures led to the PA not being pre-heated sufficiently. The faulty temperature sensor position gave the illusion that the PA temperature was in fact to the required standard (more than 140°C).
A well-trained commissioning engineer would have checked every field signal in the initial cold checks, but also had a second chance to identify the problems and inconsistent process feedback when guaranteed performance of throughput and IBA quality were not achieved.
The contractor concerned is presently experiencing financial difficulties, as many of their completed plants have warranty issues. Better training and a larger budget for the commissioning of the EfW plant would have been a more beneficial strategy for long-term financial sustainability. The information for this case study was presented by the general manager, Juergen Schaffer, at the IMechE User Group 2019 (*Ref 1).Case six: Cooperation between operator and contractor during on-line boiler cleaning
The author was supporting KRR Prostream’s explosive cleaning team in a mid-sized UK EfW plant. The target was cleaning the horizontal boiler pass from economizer bundle to super heater with detonations through boiler openings arranged along an elevated walkway, while the boiler was operating (on-line). Ultimately this allowed the operator to continue operating without shutting down the plant. In these interventions it is of utmost importance to carefully control the strength of detonation and the consequent volume of ash flow into the hoppers and through the ash transport system below.
The author’s job was to observe and advise the team and also to cooperate with the plant staff that monitor and control the flow of ash using slide valves and other ash transport equipment. The ash system valves are situated on a walkway three levels below from where the KRR team were working, with no visual line of sight; communication was via two-way radio sets and the KRR team announced which boiler section they would detonate in.
The member of staff on the operator side, tasked with controlling ash flow, known as the ashman, is advised as to which boiler section was being cleaned and in which ash hopper the ash would fall. The ashman also feeds back the volume of ash coming through the system and may stop detonation work to prevent an ash system overload.
Sometime into the clean, after a change of boiler section from the KRR team, they are surprised not to hear from the ashman (to pause detonations), especially as they can see that large volumes are removed from the tubes seen through the boiler door. When calling on the radio the ashman says, no ash is coming through the system. The team could have taken this as read and continued. However, the KRR team leader is aware of the risk of blocking the transport system, this can lead to an unplanned shutdown, and asked the author to check.
When the author got down to the ash transport level it became clear that the ashman is monitoring the wrong hopper section. When made aware of this he moves to the correct one, detecting a backlog of ash. He is then able to avert the worst-case scenario, a blockage of the ash conveying system.
This case study shows the importance of on-site plant knowledge and identification and good communications.
References
*Ref 1 Boiler User Group 2019 EfW and Biomass and Fossil Fuels, OPERATIONAL BEHAVIOUR AND EXPERIENCE AT LINCOLN EFW PLANT, Juergen Schaper, general manager, FCC Environment
About the author
Roberto Vogel is the founder and director of Vogel Waste Industry Services trading as of ENPRO SWISS, former chief commissioning engineer for Von Roll Inova (now HZI), founder and technical director of KRR ProStream (now retired) and EWB editorial panel member
