Optimizing Pump and Compressor Performance in Renewable Diesel Refining

During the pandemic, 11 refineries in the United States were shut down due to declining demand for transportation fuels of all kinds. This year, four of these refineries are returning to service and are being converted into renewable diesel refineries. Every refinery has a wide range of pumps and compressors that have been used for decades to refine traditional fuels. As these refineries come back, they are upgraded to process different and greener feedstocks. This provides operators with the perfect opportunity to update their equipment. A wide range of pump and compressor upgrades are currently being implemented at these plants to meet new requirements and optimize efficiency.

An update on renewable diesel

About 50% of the crude oil used worldwide is refined into transportation fuels, which contribute to greenhouse gas emissions. Biomass is a renewable energy source that can be blended with crude oil and converted into liquid transportation fuels.

Like ethanol, which is blended with crude to make unleaded gasoline, there is a wide range of renewable materials that can be used as feedstock for diesel. These include oils of plant origin, such as soybean oil and palm oil. Other green feedstocks, such as jatropha and algal oils, are also being evaluated as candidates to help meet the growing demand for renewable diesel around the world.

There are two main reasons why renewable diesel refining is expected to grow in the future:

  1. Renewable raw materials are less harmful to the environment.
  2. Renewable feedstocks are cheaper than crude oil, which can improve a refinery’s operating margins.

The refining process begins by pumping raw materials at high pressure into multi-stage catalytic reactors, where they are saturated and deoxygenated. The reactor effluent is separated to remove carbon dioxide (C02) and other low molecular weight hydrocarbons. The result is mixed with additional hydrogen gas and then piped to a second catalytic reactor, where diesel fuel and a branched paraffin byproduct are produced. At this stage, the hydrogen is separated via conventional gas/liquid separators. Compressors recycle excess hydrogen back to the reactor and pumps move the liquid to a distillation process, where by-products (such as propane and naphtha) are separated, and a series of flow properties to cold in the diesel are adjusted to meet the required specifications.

Refining renewable diesel is similar to traditional refining. However, the raw materials mixed in the process have different properties, and the equipment moving these materials must operate at different flow rates and pressures.

Pumps typically used in refining include American Petroleum Institute (API) single-stage and multistage integral gear pumps as well as multistage between bearing pumps. What is the best way to ensure pumps are optimized to operate at maximum efficiency? It starts with sizing the pump correctly for the required task. This is accomplished with advanced analytics and computer-tuned hydraulics, which place the Best Efficiency Point (BEP) at or slightly below the rated point, resulting in optimum efficiency. This allows the use of smaller drives, which can still provide the required power while saving energy.

For refiners switching to renewable diesel, pumps and compressors handling renewable diesel feedstock should be re-evaluated to keep them within API limits (ideally between 80% and 100% BEP). Rotating equipment operating above or below rated flow can lead to cavitation, seal failures, high vibration, and motor overloads.

Pump or compressor failures of any kind result in poor mean time between repair (MTBR), plant downtime and increased maintenance costs. It is essential to prevent this domino effect, as maintenance and operating costs can represent up to 80% of total life cycle costs.

An opportunity for plant operators to upgrade

Manufacturing improvements, combined with customer feedback from refinery operators, have identified the following 10 areas to optimize pump and compressor performance, extend maintenance intervals and reduce total cost of ownership (TCO):

1. Pump and compressor upgrades

Obsolete compressors/pumps in the field can be upgraded without changing major components, such as casing, casings and foundation.

2. Repricings

As process conditions change, pumps and compressors must be recalibrated to match flow and head to the new process requirements. Efficiency improvements are achievable without requiring a new motor, footprint or piping. Some tariffs were able to provide 30% more head with 10% power savings.

3. Gasket replacements

New materials have improved seal performance and extended seal life. Changes to seal housings improve fluid flow and eliminate high point vapor pockets, improving seal life.

4. Cartridge seal upgrades

These facilitate error-free replacement of pump shaft seals. Self-contained cartridge seals consist of a shaft sleeve, seal, and gland plate, and they are mounted to the pump shaft as a single assembly.

5. Inner and outer bearings

The latest generation of bearings provides improved rotor stability over a wider operating range. They also dampen and reduce vibrations and extend the life of seals.

6. Bearing frame upgrades

Drive end replacements improve reliability and ensure compliance with current API 610 bearing life requirements.

7. Gearbox conversion kits

These offer up to 10 design improvements via an interchangeable bolt-on assembly that provides an estimated minimum Mean Time Between Maintenance (MTBM) of five years. Gearbox swaps provide better bearing life and include stronger gear sets that facilitate greater
load levels.

8. Compressor Inlet Guide Vanes (IGV)

This is a series of vanes arranged at the inlet of a compressor that pre-swirl
gas flow entering the turbine. IGVs increase the flow rate variation of a compressor while reducing the amount of work required from the main operator.

9. High efficiency compressor turbines

Recent improvements in turbine design allow the compressors to produce the same flow, using up to 20% less energy than previous designs.

10. Instruments

Updated instrumentation for vibration and temperature monitoring gives operators peace of mind that rotating equipment is operating at BEP.

The ROI of Upgrades Vs. Purchasing New Equipment

These upgrades cover nearly 90% of the maintenance needs for rotating equipment. Upgrading key components can add decades of life. They also eliminate the cost of installing a new pump or compressor, which in refineries involves a custom process that can require unique foundations, complex piping, and crews of welders, concrete workers, and contractors. crane operators.

Each of these aftermarket upgrades can be done in days, on standard turnaround time, at a fraction of the cost of buying new gear. Benefits that come with these upgrades include:

  • Reduced operating costs: Ensuring pumps and compressors are operating at their BEP minimizes vibration and reduces energy costs.
  • Reduced maintenance costs: Upgrading key components with new warranted parts extends maintenance intervals and reduces overall maintenance costs.
  • Increased plant availability: In the coming months, refining capacity worldwide will increase. Many refineries operate around the clock, and plant availability is the true measure of all optimization efforts.

Over the past two years, much of the regularly scheduled maintenance at refineries (and plants of all types) has been pushed back due to labor constraints and lower demand during the pandemic. Today, the demand for diesel fuel is skyrocketing. Unfortunately, refined diesel inventories are at their lowest level since 1990 and prices are at all time highs.

As a result, refineries are expanding their operations to meet demand, and many refineries are integrating renewable diesel into their processes. Analyst firm International Info Resources (IIR) is currently tracking 119 planned renewable diesel unit additions globally. The majority of them will be incorporated into existing refineries.

Either of these scenarios (increasing capacity or incorporating a new process) offers the opportunity to reclassify and upgrade pumps and compressors.

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