A ScienceDirect.com abstract highlights the importance of heat exchangers in refinery energy-efficiency efforts:
Crude oil fouling in pre-heat train heat exchangers has been a major problem in oil refining for decades. The operating problems, increased energy requirements and greenhouse gases emissions, which arise from the inefficiencies caused by fouling, are discussed.
Emerson’s Tim Olsen and Gary Hawkins, whom you may recall from earlier refining-related posts, will be presenting Fouling and Heat Exchanger Monitoring at the October 2011 Emerson Exchange gathering in Nashville. Tim sent me a sneak peak of a draft of their presentation.
The refining industry team has been working with refiners to understand the many causes of production losses. Right near the top is the performance of heat exchangers. According to a presentation by Solomon Associates at the 2011 NPRA Reliability and Maintenance Conference this past spring, top tier refiners optimized the profitability of their operations through incremental improvements in reliability. Cutting reliability budgets yielded short-term gains at the expense of ongoing profitability.
Tim and Gary highlight the common problem of crude pre-heat exchanger fouling, including the heat exchanger on the incoming line to the desalter vessel and the series of heat exchangers entering the furnace, where the crude oil is heated before entering the atmospheric distillation unit.
There are several causes of crude unit pre-heat fouling including insoluble asphaltenes, inorganic foulants such as iron sulfide, sea salt, clay, and sand, low flow velocity, and insufficient cleaning operations.
A key opportunity to minimize inorganic foulants is to accurately measure the oil/water interface level in the desalter to prevent salt water going downstream to the heat exchangers. In an earlier post, Refinery Desalter Guided Wave Radar Level Measurement, I shared how this interface could be accurately measured.
Tim and Gary note that even though these heat exchangers are a major source of inefficiency, process downtime, and maintenance expense, they are rarely instrumented well enough to continuously monitor their performance. Today most measurements are conducted manually with several months between measurements the norm. Fouling and corrosion can result in millions of dollars annually in lost revenue and increased costs.
With the addition of wired or wireless flow and temperature measurement instrumentation coupled with heat transfer calculations, predictions can made and presented to the plant operators when cleaning and maintenance will be required. The heat exchangers that require attention can be scheduled for maintenance at the next turnaround or other downtime condition.
Tim and Gary cite a project where wireless instrumentation was added to a refinery crude unit along with heat exchanger modeling calculations to determine when cleaning was required. The payback for early notification and subsequent cleaning of a fouled heat exchanger was in less than 90 days.
If you’ll be at the Emerson Exchange and have heat exchangers in your process, this may be one presentation to add to your “must see” list.