Reducing refinery heater revamp costs
This article discusses the importance of being able to deliver a safe, cost-effective heater revamp, in the shortest possible shutdown
Tony Tindall, Foster Wheeler Energy
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The reasons for revamping heaters are many and include: extending fired heater working life with minimum investment; improving efficiency (eg, increasing duty or efficiency by adding air preheat); reducing environmental impact to meet noise and flue gas emission regulations, (such as NOx/CO2 reduction) and extending periods between shutdowns through improved availability and reliability.
The prolonged use of sulphurous fuels has often resulted in the corrosion of some components essential to the heater’s structural integrity.
Where the sulphur compounds in the fuel have precipitated out behind damaged refractory layers, it is common for the refractory anchors to have been severely corroded. This allows the refractory to move away from the heater walls and the acidic deposits to attack the steel casing plate and main supporting columns. This frequently results in hot spots on the outer casing of the heater, which can be evidenced by peeling casing paint or alternately, can be detected early by using thermal imaging technology.
Other common problems that are encountered include:
• Dew point corrosion of cold end surfaces and tubesheets of air pre-heaters
• Convection section extended surface tubes clogged by ash, refractories, catalyst fines or unburned fuel, leading to thermal underperformance of the convection section and subsequent lower heater efficiency. Where air pre-heaters are installed, this can lead to an increase in combustion air temperature which, in turn, can produce long burner flames in the radiant section
• Flame impingement on the radiant roof tubes and convection section tubes can, in time, cause premature failure of the cast tube supports, especially if the supports have also been exposed to fuel contaminants such as vanadium and sodium
• Tube thinning and bowing
• Damage from tramp air through heater casing and header boxes.
Almost all heater component parts
can and have been replaced on numerous revamps over the past 40 years. Safe, practical and economic solutions have been delivered for replacement pressure parts, removal and reinstallation of corroded steelwork, dis-investment of refractories containing asbestos, replacement of combustion equipment and addition of air preheat systems.
When evaluating revamp projects to establish their viability, it is wise to recruit the services of a consultant company with a proven track record of actually delivering safe, successful and cost-effective revamps. Such a company will have experienced heater thermal and mechanical engineers, as well as project managers, estimators and planners to undertake a thorough study of the various possible options available for the plant owner to consider.
Intimate knowledge of heater design is essential, as many of the older heaters were constructed in situ at the site and safe removal or modification of the corroded component parts is a skilled task. Many of these older heaters have asbestos materials in refractories and/or sealing tapes in joints, which have to be removed under strict safety procedures by specialist contractors. Factors such as plot space for lifting, piling for heavy lift equipment, logistics for modules, access and egress for plant and heavy equipment, laydown areas and site working areas all need to be considered during the initial planning and evaluation phase as they will affect cost, schedule and practicality of the various solutions.
Another essential ingredient for a successful revamp project is the early participation of all relevant personnel who will be involved in or impacted by the proposed work. It is important to involve inspection and safety personnel as well as the usual engineering, operational, and maintenance groups. During the definition of the scope of work, and especially during the planning, peer group reviews help reveal any activities or requirements hitherto not considered in the plan. Seemingly unrelated shutdown activities from other departments can have a crucial impact on the overall plan during shutdown so it is vital to ensure all groups ‘buy in’ to the project as early as possible and fully define the scope of work. Late scope definition or significant changes can severely impact on the shutdown schedule.
Cost phase 1
When estimating the overall costs and return on investment (ROI) of the various options under consideration, several aspects should be considered. Lowest in real cost but often the most cost-effective overall, is the initial study and detailed engineering and planning. It is during this phase that comparisons between, say, in situ remedial work and modular replacement will need to be made: crucial decisions that will affect the overall cost of the job. Innovation is essential to effect solutions to problems that may seem initially impractical (Figure 1).
Consideration must be given to such matters as the strength and integrity of corroded structures and the possible ways to handle these safely, or how to establish the presence of any asbestos and the procedures for its safe removal within the minimum time available. It is often possible to reduce the costs and schedule for dis-investment of materials, such as asbestos, by containing the materials within suitably strengthened and sealed modules for later safe disposal away from the immediate plot area. The relatively modest investment in thorough detailed engineering and planning made during this stage of the project is more than repaid during the shutdown and construction phase.
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