Exploring Core Pump Technology in the LPG Safety Enhancement (Maleic Anhydride) Project

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Exploring Core Pump Technology in the LPG Safety Enhancement (Maleic Anhydride) Project

Sinopec Qingdao Refining and Chemical Co., Ltd. (QRC) has rolled out the “LPG Safety Enhancement (Maleic Anhydride) Project” – a key tech upgrade and capacity expansion initiative under Sinopec. By optimizing LPG processing and maleic anhydride production units, the project has significantly enhanced the safety, efficiency, and environmental performance of unit operations. In this complex system, selecting and utilizing core pump equipment and its sealing technologies demonstrates the current technical standard of high-end fluid transfer solutions in the process industry.

Sinopec Shanghai Engineering Co., Ltd. designed the project, which covers key steps from raw material processing to product production. The media being transported include high-temperature thermal oil, flammable liquefied gas, corrosive chemicals and industrial water – all of which set very high requirements for pump equipment in terms of seal reliability, material compatibility and long-term operational stability. As a key part to stop media leakage, choosing the right pump seal systems has a direct impact on the safe and stable operation of the whole project.

The following is an analysis of the sealing solutions for typical pump types in the project, demonstrating engineering technical solutions under different operating conditions.

Absorber Bottom Circulating Pump: A Robust Choice for Corrosion Resistance

Operating Conditions: Circulates lean solvent (specific gravity 1.025) at 85℃.
Pump Body/Wetted Parts Material: A-8 (316L stainless steel)
Sealing Solution: PLAN 11 + 62
Solution Analysis:
- PLAN 11 (Self-flushing): Draws clean fluid from the pump outlet to “shower” the seal face directly, playing a core role in “cooling and lubrication” – a classic and reliable solution.
- 62 (Quenching): Injects nitrogen outside the seal to form a “gaseous barrier”, effectively preventing moisture and impurities in the air from entering, avoiding crystallization or corrosion on the outer side of the seal ring, and providing “double insurance” for long-term operation.

Absorber Overhead Circulating Pump: An Efficiency Model for High Head

Operating Conditions: Transports rich solvent (specific gravity 1.017) at 70℃.
Pump Body/Wetted Parts Material: A-7 (304L stainless steel)
Sealing Solution: PLAN 11 + 61
Note: Similar to the P-2410 operating conditions but with higher head requirements, the selection emphasizes efficiency. The sealing solution is also based on PLAN 11, with the PLAN 61 (quenching) solution as a standard safety configuration to ensure stable operation under high-head conditions.

For Medium-Temperature Corrosive Solvent Conditions

Typical Media: Organic solvents such as lean solvent and rich solvent, 70~85℃, with slight corrosiveness.
Solution: PLAN 11 + 62 / 61
Solution Analysis:
- PLAN 11 (Self-flushing): Draws media from the pump outlet to flush the seal face directly, providing cooling and lubrication – a basic solution for handling clean or slightly contaminated fluids.
- PLAN 62 (Nitrogen Quenching): Suitable for scenarios requiring prevention of crystallization or corrosion on the atmospheric side, isolating air through a nitrogen barrier.
- PLAN 61 (Nitrogen Purging + Leak Monitoring): Combines gas sealing and leak monitoring functions, suitable for scenarios with higher reliability requirements.
Application Scenarios: Solvent circulation, absorbent fluid transfer, and other low-corrosiveness but long-term operation conditions.

Stripper Reboiler Circulating Pump: A “Cooling Expert” Resisting 193℃

Operating Conditions: Transports DBP + maleic anhydride mixture (specific gravity not specified) at 193℃ – the “high-temperature champion” in the project.
Pump Body/Wetted Parts Material: A-8 (316L stainless steel)
Sealing Solution: PLAN 21 + 53A
Solution Analysis:
High temperature is the enemy of seals, which can directly damage seal components.
- o PLAN 21 (Flushing with Cooler): This is crucial because the external cooler ensures that the high-temperature flushing fluid operates at a safe temperature by cooling it before injecting it into the seal cavity.
- o +53A (Barrier System with Cooling): This double-seal design isolates the high-temperature medium entirely by injecting cooled, clean barrier fluid in between the two seals. There won’t be any leaks even if the initial seal fails.

For High-Temperature Heat Medium and Crystallizable Media Conditions

Typical Media: DBP + maleic anhydride, heat transfer oil, etc., >150℃, prone to coking or polymerization.
Solution: PLAN 21 + 53A
Solution Analysis:
- PLAN 21 (Self-flushing with Cooler): Reduces the temperature of flushing fluid through a heat exchanger to prevent seal failure caused by high temperature.
- PLAN 53A (Pressurized Double Barrier Seal System): Creates a dependable barrier by adopting a double-seal structure and injecting cooled barrier fluid into the seal cavity at a pressure greater than the pump cavity. Zero media leakage is guaranteed by the secondary seal, even in the event that the first seal fails.
Application Scenarios: Reboilers, reactor feed pumps, high-temperature heat transfer fluid circulating pumps, etc.

Tempered Water Circulating Pump: A Cost-Effective and Reliable “Pragmatist”

Operating Conditions: Transports industrial water at 53℃ – clean and mild.
Pump Body/Wetted Parts Material: S-6 (cast iron)
Sealing Solution: PLAN 11 + 61
Solution Analysis:
For clean cold water, no complex solution is needed; simple PLAN 11 flushing is perfectly sufficient. The +61 (quenching) here is more of a standard configuration or precautionary step, reflecting the design principle of pursuing extreme economy while meeting safety criteria.

For Clean and Mild Media Conditions

Typical Media: Industrial water, cooling water, low-viscosity oil products, <60℃, clean and free of solids.
Solution: PLAN 11 + 61 (or single seal)
Solution Analysis:
Basic self-flushing (PLAN 11) meets cooling and lubrication needs, with simple structure and low cost. Adding PLAN 11 mainly serves as a preventive measure to cope with unexpected working conditions or improve reliability as a standard configuration.
Application Scenarios: Tempered water, cooling water, clean raw material transfer, and other low-risk conditions.

Feed Pump: The “Ultimate Bodyguard” for Flammable and Explosive Substances

Operating Conditions: Transports propane and butane liquefied gas (specific gravity only 0.47) at 41.8℃, with high inlet pressure and high vaporization tendency.
Pump Body/Wetted Parts Material: A-8 (316L stainless steel)
Sealing Solution: PLAN 11 + 72 + 76
Solution Analysis:
This is one of the highest safety-level configurations, adopting a double mechanical seal.
- +72 (Buffer Fluid System): Injects clean buffer fluid (e.g., ethylene glycol) with higher pressure between the two seals. Thus, if the inner seal fails, the leaked substance is safe buffer fluid rather than dangerous liquefied gas, achieving intrinsic safety.
- +76 (Leak Collection System): Specifically collects and monitors micro-leaks of buffer fluid and triggers an alarm to remind maintenance.

For High-Pressure Flammable and Explosive Media Conditions

Typical Media: Liquefied Petroleum Gas (LPG), propane, light hydrocarbons, etc. – easy to vaporize and explode.
Solution: PLAN 11 + 72 + 76
Solution Analysis:
- PLAN 72 (Buffer Fluid Injection System): Injects buffer fluid with pressure higher than the pump cavity between the double seals (e.g., ethylene glycol), ensuring the leakage direction is from buffer fluid to pump interior, achieving intrinsic safety.
- PLAN 76 (Leak Collection and Alarm): Monitors buffer fluid leakage in real time, triggers alarms promptly, and supports predictive maintenance.
Application Scenarios: LPG feed pumps, light hydrocarbon transfer pumps, reactor feed pumps, and other high-risk occasions.

Molten Salt Pump: A “Fearless Warrior” Resisting Extreme High Temperatures

Operating Conditions: Transports molten salt (specific gravity ~1.9) – the medium is extremely hot and prone to solidification; it will freeze into a solid once the pump stops.
Pump Body/Wetted Parts Material: C-6 high-temperature Cr-Ni alloy steel
Sealing Solution: Packing Seal / Self-flushing for Plain Bearings
Solution Analysis:
Under extreme high-temperature conditions, the elastic components of traditional mechanical seals fail, so the more traditional packing seal is selected.
- Packing Seal: Made of high-temperature graphite braid, allowing controlled micro-leakage; the small amount of leaked molten salt just lubricates and cools the packing and shaft sleeve.
- Self-flushing System: Draws a stream of high-temperature molten salt from the pump outlet to directly flush and lubricate the plain bearings inside the pump. Since no lubricating oil can work at 400℃, only the medium itself can be used for lubrication.

For Extreme High-Temperature and Solidifiable Media Conditions

Typical Media: Molten salt, high-temperature asphalt, sulfur, etc. – >300℃, prone to solidification when shut down.
Solution: Packing Seal + Self-flushing System
Solution Analysis:
Packing Seal: Uses high-temperature graphite or alloy fiber packing, allowing micro-leakage to lubricate and cool the shaft sleeve.
Self-flushing: Draws high-temperature media from the pump outlet to lubricate bearings and stuffing boxes, avoiding the use of external lubricating oil (prone to carbonization).
Design Feature: Sacrifices “zero leakage” for reliability and anti-solidification capability, suitable for ultra-high-temperature conditions where traditional mechanical seals are incompetent.
Application Scenarios: Molten salt systems, asphalt transfer, high-temperature heat transfer, etc.

The engineering concept that “details determine success or failure” is aptly embodied in the pump selection for Qingdao Refining & Chemical’s maleic anhydride project. Each PLAN number is a collection of clever, methodical engineering solutions that are not just simple equipment assemblies but also reflect a thorough understanding of media characteristics and operating conditions, as well as the ultimate goal of safety and environmental protection.

The stable operation of the complete large-scale unit in the project has been guaranteed by Longgang Pump Industry, offering the strongest foundational support for the growth of the chemical industry and the nation’s energy security.

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