Refineries generally adhere to the "if it’s not broken, don’t fix it" philosophy, and rightly so. They handle a high-volume mix of hot, toxic, corrosive and explosive fluids and gases at high pressure all day, every day. Nevertheless, times change, technologies change and even things that "aren’t broken" often can be made more efficient and safer.
Current filtration of feedstocks and process chemicals might not be broken, but today’s clean-in-place technologies can increase both safety and productivity. As an added benefit, they also can reduce a refinery’s carbon footprint and overall environmental impact. New clean-in-place filtration systems, such as for amine filtration and catalyst protection, have proven their advantages in hundreds of refineries around the world.
With or without cartridges
Virtually every refinery is facing or will face a need to process sour crude in the near future. As a result, the efficiency and uptime of the amine units used to remove hydrogen sulfide (H2S) and carbon dioxide (CO2) from feedstocks before refining will become increasingly critical to the overall productivity of the refinery.
To consider the process in principle, a lean amine, which usually is either diethanolamine (DEA), monoethanolamine (MEA) or methyldiethanolamine (MDEA), reacts with the H2S and CO2 in the feedstock to create a rich amine that is regenerated and reused in a continuous process. As it circulates, the amine picks up a wide range of contaminants in addition to H2S and CO2. These typically include pipe scale, rust, iron sulfide, sand and other solids that foul flash drums, heat exchangers, strippers, reboilers and carbon filters. Many of these contaminants also attract hydrocarbons, which cause system foaming that reduces process efficiency.
Today’s most common amine filtration solution is a cartridge-type filter in the lean amine stream after regeneration. The problem with this approach is that everything upstream of the regenerator is exposed to a full load of contaminants.
Filtering the rich amine stream is a better solution for protecting the equipment, but it can create a safety hazard because operators may be exposed to dangerous and potentially explosive H2S and other hazards while changing cartridges. In addition to the continuous expense of replacement cartridges, the used cartridges must be disposed as hazardous waste, which creates another set of costs and environmental impacts.
By contrast, a clean-in-place solution built around a backwash filtration system comes with none of these negative impacts. Designed specifically for filtering the rich amine stream, these systems typically use a combination of water back flush and inert gas purge to avoid contaminating the amine.
With this solution, an operator is less likely to be exposed to toxic gases or other potentially dangerous materials, and the waste produced might, or might not, require disposal as hazardous materials. Moreover, no bags or cartridges need be purchased, no material must be inventoried and tracked, and maintenance and handling costs are greatly reduced. During a 10-year period, a clean-in-place solution can save up to 60 percent of the cost of a disposable media system.
Modern clean-in-place filter systems use backwash technology to remove contaminants trapped by the filter media. Backwashing works best when the contaminants accumulate on the surface of the media rather than being trapped inside. This requires a filter design with the lowest possible flux rate — or the rate of flow through a specific filter area — to meet application requirements. Reducing the flux rate lowers the velocity of the fluid as it passes through the media, reducing the force with which particles impinge on it.
Increasing active filter surface area is the most efficient way to achieve a low flux rate. To do so, a filter element with multiple small diameter tubes can be made of woven wire or slotted wedge to meet application requirements.
Filters operating at low flux rates tend to create a porous particulate cake on the surface of the media. This cake improves particulate removal efficiency and extends the period between cleaning. As the cake builds, it increases the pressure differential across the filter element and triggers the back flushing cycle when it reaches a pre-determined value. During that operation, the filter bank is isolated from the feed flow and purged.
The best practice is to clean the filter elements individually so that the total backwash energy is applied to each element. A system with multiple parallel filter banks allows continuous flow while the individual banks are off-line for cleaning.
Protection for catalyst beds
Rich amine filtration is not the only process that can be improved with clean-in-place filtration. Another candidate, catalyst beds, accelerates cracking long-chain hydrocarbons into more useful lighter forms.
The beds are costly and prone to contamination from particulates contained in the feed stocks, and the entire process must be shut down for maintenance or catalyst replacement. Either process can expose workers to potentially dangerous conditions, and when the catalyst is replaced, the waste must be disposed in an environmentally safe way.
To mitigate these issues, a catalyst protection filter removes contaminants from the feedstock and significantly extends the useful life of the catalyst bed. Like with amine filtration, clean-in-place systems are efficient, cost-effective ands safe, and they are being installed across the country.
Additionally, similar solutions can remove particulate and other contaminants from the heavy, corrosive residual feedstocks for coking operations. Clean-in-place systems for coker gas oils must be stronger than typical catalyst protection filters to handle their higher temperatures and pressures, but the operating principles and benefits are essentially the same.
Safer, more efficient solution
Clean-in-place technology offers a safer process than bag or cartridge filtration in addition to being cost effective and having other benefits. From an environmental perspective, eliminating filter bags and cartridges from a waste stream reduces the refinery’s impact on landfills. In addition, continuously removing contaminants extends the life of system components while reducing maintenance requirements and unscheduled downtime. With this change, the system is more productive and less expensive to operate.
Cartridge filtration and catalyst protection systems in amine units might not be broken, but clean-in-place filtration systems can make those operations more efficient; more environmentally friendly; and, most important of all, safer.
Mike Isch is the global refinery segment manager for Eaton Hydraulics’ Filtration division.