Case StudiesThis is a mechanical seal upgrade case study about applying advanced upstream pumping technology instead ofconventional tandem seal arrangements with external flushing in high corrosive fluid pump seal applications in order to improve equipment reliability and minimize the operating cos

FitzGibbon, Gibbon

Yanhui, XU

English

Texas A&M University

  
Copyright© 2018 by Turbomachinery Laboratory, Texas A&M Engineering Experiment Station 
 
Applying Upstream Pumping Sealing Technology for high corrosive fluid – Improve Reliability & Operating Cost 
 
 
 
 
XU Yanhui 
Engineering Director 
John Crane  
Tianjin, China 
 
 
 
 
 
 
 
 
Gibbon FitzGibbon 
Manager, High Duty & Specialty Product Group 
John Crane 
Manchester, United Kingdom 
 
 
 
Xu Yanhui is the director of engineering in 
John Crane China. He graduated with Master 
Degree in Chemical Process Machinery from 
Tianjin University in China, since then he 
worked in mechanical seal industry in 
various roles of engineering. He is the 
technical member of multiple industrial 
committees in China.  
 
 
Gibbon FitzGibbon is the manager of the 
High Duty & Specialty Product Group for 
wet seals global engineering, John Crane, in 
Manchester, UK. He has been working with 
mechanical seals in a variety of roles since 
graduating with a BSc in Mechanical 
Engineering from the University of Glasgow, 
first with Flexibox International and then 
with John Crane. He is a Chartered Engineer and member of 
the Institution of Mechanical Engineers. 
 
 
 
ABSTRACT 
 
 This is a mechanical seal upgrade case study about 
applying advanced upstream pumping technology instead of 
conventional tandem seal arrangements with external flushing 
in high corrosive fluid pump seal applications in order to 
improve equipment reliability and minimize the operating cost. 
   
INTRODUCTION 
 
 This real case occurred in an Acetyls plant in China. This 
plant produces acetic acid and acetate.  
 The equipment is a centrifugal pump transporting an 
organic fluid with undefined properties. This process fluid is 
very special for the plant as it is highly corrosive and 
furthermore contamination is not allowed. The process fluid has 
relatively high temperature, high pressure and poor lubrication 
characteristic.  
 
EQUIPMENT & APPLICATION DUTY 
 
Pump type: Overhung centrifugal pump 
Suction pressure: 2.81 - 2.82 MPa g (407 - 409 psi g) 
Discharge pressure: 3.35 - 3.48 MPa g (486 - 505 psi g) 
Shaft speed: 1500 RPM 
Process fluid: Organic fluid 
Process temperature: 50 - 189 °C (122 - 372 °F) 
Viscosity: 0.636 - 0.188 cP 
Vapor pressure: 2.35 - 2.80 MPa g (341 - 406 psi g) 
Specific Gravity: 0.823 - 1.013 
Special requirement: process contamination is not allowed. 
Only pure acetic acid or very limited quantity of demineralized 
water are accepted to be mixed.  
 
ORIGINAL SEAL SOLUTION & ISSUE 
 
 The original mechanical sealing arrangement was a tandem 
unpressurized seal with API 682 plan 32/52 system as shown in 
Figure 1. Plan 32 external flushing was pure acetic acid. The 
reason for using an unpressurized tandem seal was to prevent 
the barrier fluid contaminating the process fluid. Plan 32 was 
selected for the inboard seal flushing was due to the high 
process pressure and low margin above vapor pressure of the 
process fluid pressure. To ensure the inboard seal had good 
lubrication, external flushing was specified.  
 From a technical and application aspect, this seal solution 
has been used before on many other similar plant and it is a 
default solution from EPC side as well. But there are a few 
issues with this seal solution including: 
 High initial cost for the seal and system 
Pure acetic acid is a very corrosive fluid and requires all 
the wetted material to be Zirconium or Alloy-C. All the 
  
Copyright© 2018 by Turbomachinery Laboratory, Texas A&M Engineering Experiment Station 
O-rings were required to be FFKM (perfluoroelastomer) 
material. In addition, as it is an unpressurized flushing 
plan, the inboard seal leakage will continuously mix with 
the buffer fluid, so the API Plan 52 system piping material 
needs to be anti-corrosive.  
 High operating cost 
The process fluid requires the API plan 32 to be pure 
acetic acid. The flowrate required is 23 liters per minute (6 
US gallons per minute) continuously, and the flushing 
pressure shall be 2 bar (30 psi) above the seal chamber 
pressure. Pure acetic acid is the final product of the plant, 
so having the final product flush back to the mid-process 
in the plant adds cost and also reduces the process 
efficiency. Especially when the market for acetic acid is 
growing, this seal solution becomes less cost-effective.  
 Reliability  
As the process fluid is tending to vaporize, so external 
flushing pure acetic acid was introduced to the seal 
chamber in order to keep the inboard seal cool and 
lubricated. But if the acetic acid source pressure or flow is 
unstable, the inboard seal will see high temperature 
process fluid and may experience vaporization and dry 
running. The chamber pressure may be up to 30 bar g (435 
psi g), which is a fairly high pressure in chemical plant, so 
it is not easy to find and maintain a constant source of plan 
32 fluid at high pressure. This reduces seal reliability, and 
it often fails within one year. 
 Environmental & health issue 
Acetic acid is a weak acid but is may react violently when 
in contact with other substances (International Program on 
Chemical Safety, 2010). For this seal solution, acetic acid 
used for external flushing will leak out through inboard 
seal faces and into the plan 52 buffer fluid. Eventually 
some acetic acid will leak through the outboard seal faces 
to atmosphere. Under certain conditions, the leakage may 
become concentrated in liquid form, or vaporized. 
Concentrated acetic acid is corrosive to skin and may 
cause permanent eye damage and irritation to the mucous 
membranes (Centers for Disease Control and Prevention, 
1992). These burns or blisters may not appear until hours 
after exposure.  
 
Figure 1. Original Tandem Seal (courtesy of John Crane) 
 
SEAL UPGRADE SOLUTION 
 
 The upgraded seal is a high-integrity Upstream Pumping 
seal cartridge using our proven active lift technology within the 
inboard seal; this uses a low pressure liquid source (buffer fluid) 
circulated on the inside diameter of the seal face.  
 Upstream pumping technology introduction 
 A conventional mechanical seal has lapped faces to within 
2 light bands flatness. It operates by utilizing the process fluid 
as the interface film between the seal faces. The hydrodynamic 
action of the seal allows a gap of usually < 1 micron to form 
between the seal faces. This inter face film lubricates, cools and 
minimizes mechanical contact. The interface fluid should 
therefore be stable and clean to allow a good interface film to 
form and provide a long and reliable seal life. This principle 
ensures that any leakage that may occur is from the high 
pressure (product) side to the low pressure (atmospheric) side. 
 Active lift technology uses grooves on one of the seal faces 
to generate pressure between the seal rings so that they 
physically separate and operate in non-contacting mode. The 
most well-known use of this is for dry gas seals, where a barrier 
gas at a higher pressure than the sealed pressure is used to 
separate the faces. 
 Upstream pumping also uses active lift technology and is 
so called because the conventional seal face lubrication 
principle is reversed and a chosen unpressurised liquid is 
pumped from the low pressure side to the high pressure process 
fluid. This fluid must be clean and lubricating, and is typically 
water or a light oil, but even clean filtered seawater may be 
employed as this barrier liquid. Because liquid is more dense 
than gas, the pressure generated by the grooves is several orders 
of magnitude greater than that in gas seals; typically tens or 
even hundreds of bar. 
 Upstream pumping is a unique, patented (US4290611 A) 
John Crane seal technology. By utilizing specially optimized 
spiral grooves on the seal face in a liquid environment a 
pumping effect takes place between the sealing face. This has 
the effect of raising the pressure of the liquid between the seal 
  
Copyright© 2018 by Turbomachinery Laboratory, Texas A&M Engineering Experiment Station 
faces to above that of the process. The seal acts like a 
pressurized dual seal without the need to pressurize the barrier 
fluid. 
 The USP face design generates a positive pressure across 
the seal face from inside diameter to outside diameter, i.e. from 
the buffer fluid into the process fluid in the seal chamber. The 
low pressure buffer fluid is sealed by a containment seal 
operating at the preset buffer fluid pressure but capable of 
containing the primary sealed pressure in the event of an 
inboard seal failure, fully designed as a bespoke engineered 
cartridge design as shown in Figure 4. 
• Inboard Seal- Active lift technology 
 Seals using active lift technology are designed to provide 
reliable service for refineries, chemical/petrochemical 
processing, water treatment, mining, pulp and paper, and other 
industries where chemicals, low lubricity liquids, caustics, sour 
water, abrasives, slurries, and toxic products are pumped. 
 By utilizing specially optimized spiral grooves on the seal 
face in a liquid environment, a pumping effect takes place 
between the sealing faces (Figure 2). This has the effect of 
raising the pressure of the liquid between the seal faces to 
above that of the process. The seal acts like a pressurized dual 
seal without the need to pressurize the buffer fluid. (Figure 3) 
 The advantage of using an upstream pumping seal is that it 
no longer requires the use of a continuous plan 32 external 
flush. Also, the buffer fluid can be demineralized water at 
ambient temperature, which is easy to source from the plant and 
EHS-friendly.  
 Upstream pumping seals can generate greater than 40 bar 
pressure differential across the seal faces, and the upstream 
pumping rate will typically be less than 1 liter per hour (0.005 
gallons per minute). 
 For this particular application, process fluid temperature is 
up to 189 °C (372 °F), so extra cooling for the buffer water is 
required in order to avoid vaporization across the grooved faces. 
The spiral grooves are optimized for liquid phase, if it runs on a 
gas then the seal faces will contact and fail. The cooling 
requirement is considered in the system design.  
 
Figure 2: Mating Ring with Spiral Groove and its Pressure 
Profile (courtesy of John Crane) 
 
Figure 3: Leakage Direction for Pressurized Dual and Upstream 
Pumping Seals (courtesy of John Crane) 
 
 
Figure 4: Upstream Pumping Seal (courtesy of John Crane) 
 
• Outboard Seal- Containment function 
 The main function is to contain the buffer fluid in normal 
operation and in standby. And additionally to prevent major 
leakage of pumped product should the primary seal fail; the 
outboard seal is a back-up safety seal. It will run on the process 
liquid at seal chamber pressure long enough to allow a 
controlled shut down of the pump.  
• Seal system- Special Plan52M 
 The system is used to provide a pressurized buffer fluid, at 
a lower pressure than the stuffing box to the space between the 
inboard and outboard seal of a 588USP cartridge. 
 As shown in Figure 5, this System uses a hydraulic 
accumulator to absorb any thermal expansion by the fluids in 
the seal loop and seal chamber. It also maintains a pressurized 
buffer fluid to serve as a reservoir to replenish seal leakage for 
a period of time if the make-up system is off line. The stored 
buffer fluid is piped to the local seal chamber circulation and 
cooling loops, where a pumping device is attached to the 
rotating element of the inboard seal. This pumping device 
circulates buffer fluid around the sealant system and the heat 
generated in the seal chamber by both the inboard and outboard 
seals is removed by this fluid circulation. It also ensures cooled 
liquid is available to be drawn into the spiral grooves, and 
removes any vapor or air present in the seal. Additional cooling 
  
Copyright© 2018 by Turbomachinery Laboratory, Texas A&M Engineering Experiment Station 
is required for this application and a water cooler has been 
included in the scope to be installed into the seal chamber 
pipework. 
 The system is connected with site available demineralized 
water source, and the customer will ensure the water supply is 
continuous all the time. For upstream pumping technology, a 
stable, continuous liquid consumption source is critical. 
Generally all the sites have low temperature water utility.  
 
 
Figure 5: Seal System for Upstream Seal (courtesy of John 
Crane)  
Note: SG: Sight Glass; PSH- pressure switch High; PI-pressure 
indicator; PSL-pressure switch Low; F-flush port 
 
 Another key consideration on system design is sufficient 
cooling in order to bring the water circulation balance 
temperature down below 60 °C (140 °F). The reason for this is 
that the lubrication property of water becomes poor when the 
temperature is higher, which will impact outboard contacting 
seal. The other reason is to minimize the risk of scale forming 
in the water and depositing on the shallow spiral grooves of the 
inboard seal face, which could reduce pumping efficiency and 
cause the seal faces to contact and failure.  
Most upstream pumping applications have the buffer fluid at 
atmospheric pressure or perhaps at a few meters head. But in 
this application case, because of the heat soak from the high 
process temperature, if the cooling system failed there was a 
risk that the buffer fluid could get hot enough to vaporize, 
which would lead to a reduced seal life. Therefore, the buffer 
fluid system is pressurized to a few bar, to ensure it stays 
liquid. 
 
ADVANTAGE OF UPSTREAM PUMPING SOLUTION 
 
 Comparing the original and upgrade seal solution, there are 
several advantages as follows: 
 Firstly upstream pumping solution has been demonstrated 
to be more reliable and have longer MTBF 
(Mean-Time-Between-Failure) than single or even 
conventional dual seals on similar duties. The upgraded 
seal has run for at least 3 years in contrast to 1 year for the 
original seal. Upstream pumping uses non-contacting seal 
active lift technology; the stiff liquid film between sealing 
faces generates less heat than a normal contacting seal, and 
it is more tolerant of transient conditions that may occur in 
the equipment and process operation. Upstream pumping 
seal uses a low pressure water barrier (compared to a dual 
pressurized seal), this reduces the load on and heat 
generation of the outboard contacting seal, and ensures it 
runs well lubricated and under low stress, which extends 
the running life of the overall cartridge seal. 
 Secondly the upgraded solution has reduced the EHS 
(Environment, Health, and Safety) risk. Upstream pumping 
seal performs like a dual pressurized seal, so it’s “ZERO” 
emission solution. In addition, the acetic acid external flush 
was eliminated and water buffer is used, so the only 
leakage from the seal when running normally is water, not 
product. 
 Thirdly the initial cost and operating cost of the upgraded 
seal solution is lower than original one. In principle, the 
outboard seal can use normal stainless steel material as it is 
not wetted, whereas on the original seal all the metal parts 
had to be high grade anti-corrosion material. For this 
particular case, the special grade material was still used 
because of customer requirement. Also, the upstream 
pumping seal doesn’t need a continuous acetic acid flush, 
saving more cost.  
 Finally, more generally Upstream Pumping seals are a 
cost-effective alternative to both dual unpressurized and 
dual pressurized seals. While the initial cost of the seal and 
support system is broadly similar (it may be less in some 
circumstances), the payback is in the increased reliability 
and up-time of equipment, and reduction in routine 
maintenance time and effort that USP seals can offer. 
 
CONCLUSIONS 
 
Upstream pumping technology offers several advantages 
compared to conventional seal arrangements, especially for 
certain special applications. It offers increased reliability and 
reduced environmental impact. Its attractiveness is increased as 
it requires only a simple auxiliary system (fundamentally just a 
water supply) even though it offers it’s a more reliable seal 
performance.  
Except for this case, upstream pumping products are also 
designed to provide reliable service in refineries, 
chemical/petrochemical processing, water treatment, mining, 
pulp & paper, and other industries where chemicals, low 
lubricity liquids, caustics, sour water, slurries and toxic 
products are pumped.  
 
REFERENCES 
  
Copyright© 2018 by Turbomachinery Laboratory, Texas A&M Engineering Experiment Station 
 
International Programme on Chemical Safety (2010), Acetic 
Acid ICSC: 0363 [Online] 5 June 2010. Available at 
http://www.inchem.org/documents/icsc/icsc/eics0363.htm 
(Accessed 2017/9/16) 
 
Centers for Disease Control and Prevention (1992), 
Occupational Safety and Health Guideline for Acetic Acid 
(Online). Available at 
https://www.cdc.gov/niosh/docs/81-123/pdfs/0002-rev.pdf 
(Accessed 2017/9/16) 
 
 
API 682, 2014, “Pumps - Shaft Sealing Systems for Centrifugal 
and Rotary Pumps,” Fourth Edition, American 
Petroleum Institute, Washington, D.C. 


Applying Upstream Pumping Sealing Technology for high corrosive fluid – Improve Reliability & Operating Cost

Texas A&amp;M Repository

  Copyright© 2018 by Turbomachinery Laboratory, Texas A&M Engineering Experiment Station  Applying Upstream Pumping Sealing Technology for high corrosive fluid – Improve Reliability & Operating Cost     XU Yanhui Engineering Director John Crane  Tianjin, China         Gibbon FitzGibbon Manager, High Duty & Specialty Product Group John Crane Manchester, United Kingdom    Xu Yanhui is the director of engineering in John Crane China. He graduated with Master Degree in Chemical Process Machinery from Tianjin University in China, since then he worked in mechanical seal industry in various roles of engineering. He is the technical member of multiple industrial committees in China.    Gibbon FitzGibbon is the manager of the High Duty & Specialty Product Group for wet seals global engineering, John Crane, in Manchester, UK. He has been working with mechanical seals in a variety of roles since graduating with a BSc in Mechanical Engineering from the University of Glasgow, first with Flexibox International and then with John Crane. He is a Chartered Engineer and member of the Institution of Mechanical Engineers.    ABSTRACT   This is a mechanical seal upgrade case study about applying advanced upstream pumping technology instead of conventional tandem seal arrangements with external flushing in high corrosive fluid pump seal applications in order to improve equipment reliability and minimize the operating cost.    INTRODUCTION   This real case occurred in an Acetyls plant in China. This plant produces acetic acid and acetate.   The equipment is a centrifugal pump transporting an organic fluid with undefined properties. This process fluid is very special for the plant as it is highly corrosive and furthermore contamination is not allowed. The process fluid has relatively high temperature, high pressure and poor lubrication characteristic.   EQUIPMENT & APPLICATION DUTY  Pump type: Overhung centrifugal pump Suction pressure: 2.81 - 2.82 MPa g (407 - 409 psi g) Discharge pressure: 3.35 - 3.48 MPa g (486 - 505 psi g) Shaft speed: 1500 RPM Process fluid: Organic fluid Process temperature: 50 - 189 °C (122 - 372 °F) Viscosity: 0.636 - 0.188 cP Vapor pressure: 2.35 - 2.80 MPa g (341 - 406 psi g) Specific Gravity: 0.823 - 1.013 Special requirement: process contamination is not allowed. Only pure acetic acid or very limited quantity of demineralized water are accepted to be mixed.   ORIGINAL SEAL SOLUTION & ISSUE   The original mechanical sealing arrangement was a tandem unpressurized seal with API 682 plan 32/52 system as shown in Figure 1. Plan 32 external flushing was pure acetic acid. The reason for using an unpressurized tandem seal was to prevent the barrier fluid contaminating the process fluid. Plan 32 was selected for the inboard seal flushing was due to the high process pressure and low margin above vapor pressure of the process fluid pressure. To ensure the inboard seal had good lubrication, external flushing was specified.   From a technical and application aspect, this seal solution has been used before on many other similar plant and it is a default solution from EPC side as well. But there are a few issues with this seal solution including:  High initial cost for the seal and system Pure acetic acid is a very corrosive fluid and requires all the wetted material to be Zirconium or Alloy-C. All the   Copyright© 2018 by Turbomachinery Laboratory, Texas A&M Engineering Experiment Station O-rings were required to be FFKM (perfluoroelastomer) material. In addition, as it is an unpressurized flushing plan, the inboard seal leakage will continuously mix with the buffer fluid, so the API Plan 52 system piping material needs to be anti-corrosive.   High operating cost The process fluid requires the API plan 32 to be pure acetic acid. The flowrate required is 23 liters per minute (6 US gallons per minute) continuously, and the flushing pressure shall be 2 bar (30 psi) above the seal chamber pressure. Pure acetic acid is the final product of the plant, so having the final product flush back to the mid-process in the plant adds cost and also reduces the process efficiency. Especially when the market for acetic acid is growing, this seal solution becomes less cost-effective.   Reliability  As the process fluid is tending to vaporize, so external flushing pure acetic acid was introduced to the seal chamber in order to keep the inboard seal cool and lubricated. But if the acetic acid source pressure or flow is unstable, the inboard seal will see high temperature process fluid and may experience vaporization and dry running. The chamber pressure may be up to 30 bar g (435 psi g), which is a fairly high pressure in chemical plant, so it is not easy to find and maintain a constant source of plan 32 fluid at high pressure. This reduces seal reliability, and it often fails within one year.  Environmental & health issue Acetic acid is a weak acid but is may react violently when in contact with other substances (International Program on Chemical Safety, 2010). For this seal solution, acetic acid used for external flushing will leak out through inboard seal faces and into the plan 52 buffer fluid. Eventually some acetic acid will leak through the outboard seal faces to atmosphere. Under certain conditions, the leakage may become concentrated in liquid form, or vaporized. Concentrated acetic acid is corrosive to skin and may cause permanent eye damage and irritation to the mucous membranes (Centers for Disease Control and Prevention, 1992). These burns or blisters may not appear until hours after exposure.   Figure 1. Original Tandem Seal (courtesy of John Crane)  SEAL UPGRADE SOLUTION   The upgraded seal is a high-integrity Upstream Pumping seal cartridge using our proven active lift technology within the inboard seal; this uses a low pressure liquid source (buffer fluid) circulated on the inside diameter of the seal face.   Upstream pumping technology introduction  A conventional mechanical seal has lapped faces to within 2 light bands flatness. It operates by utilizing the process fluid as the interface film between the seal faces. The hydrodynamic action of the seal allows a gap of usually < 1 micron to form between the seal faces. This inter face film lubricates, cools and minimizes mechanical contact. The interface fluid should therefore be stable and clean to allow a good interface film to form and provide a long and reliable seal life. This principle ensures that any leakage that may occur is from the high pressure (product) side to the low pressure (atmospheric) side.  Active lift technology uses grooves on one of the seal faces to generate pressure between the seal rings so that they physically separate and operate in non-contacting mode. The most well-known use of this is for dry gas seals, where a barrier gas at a higher pressure than the sealed pressure is used to separate the faces.  Upstream pumping also uses active lift technology and is so called because the conventional seal face lubrication principle is reversed and a chosen unpressurised liquid is pumped from the low pressure side to the high pressure process fluid. This fluid must be clean and lubricating, and is typically water or a light oil, but even clean filtered seawater may be employed as this barrier liquid. Because liquid is more dense than gas, the pressure generated by the grooves is several orders of magnitude greater than that in gas seals; typically tens or even hundreds of bar.  Upstream pumping is a unique, patented (US4290611 A) John Crane seal technology. By utilizing specially optimized spiral grooves on the seal face in a liquid environment a pumping effect takes place between the sealing face. This has the effect of raising the pressure of the liquid between the seal   Copyright© 2018 by Turbomachinery Laboratory, Texas A&M Engineering Experiment Station faces to above that of the process. The seal acts like a pressurized dual seal without the need to pressurize the barrier fluid.  The USP face design generates a positive pressure across the seal face from inside diameter to outside diameter, i.e. from the buffer fluid into the process fluid in the seal chamber. The low pressure buffer fluid is sealed by a containment seal operating at the preset buffer fluid pressure but capable of containing the primary sealed pressure in the event of an inboard seal failure, fully designed as a bespoke engineered cartridge design as shown in Figure 4. • Inboard Seal- Active lift technology  Seals using active lift technology are designed to provide reliable service for refineries, chemical/petrochemical processing, water treatment, mining, pulp and paper, and other industries where chemicals, low lubricity liquids, caustics, sour water, abrasives, slurries, and toxic products are pumped.  By utilizing specially optimized spiral grooves on the seal face in a liquid environment, a pumping effect takes place between the sealing faces (Figure 2). This has the effect of raising the pressure of the liquid between the seal faces to above that of the process. The seal acts like a pressurized dual seal without the need to pressurize the buffer fluid. (Figure 3)  The advantage of using an upstream pumping seal is that it no longer requires the use of a continuous plan 32 external flush. Also, the buffer fluid can be demineralized water at ambient temperature, which is easy to source from the plant and EHS-friendly.   Upstream pumping seals can generate greater than 40 bar pressure differential across the seal faces, and the upstream pumping rate will typically be less than 1 liter per hour (0.005 gallons per minute).  For this particular application, process fluid temperature is up to 189 °C (372 °F), so extra cooling for the buffer water is required in order to avoid vaporization across the grooved faces. The spiral grooves are optimized for liquid phase, if it runs on a gas then the seal faces will contact and fail. The cooling requirement is considered in the system design.   Figure 2: Mating Ring with Spiral Groove and its Pressure Profile (courtesy of John Crane)  Figure 3: Leakage Direction for Pressurized Dual and Upstream Pumping Seals (courtesy of John Crane)   Figure 4: Upstream Pumping Seal (courtesy of John Crane)  • Outboard Seal- Containment function  The main function is to contain the buffer fluid in normal operation and in standby. And additionally to prevent major leakage of pumped product should the primary seal fail; the outboard seal is a back-up safety seal. It will run on the process liquid at seal chamber pressure long enough to allow a controlled shut down of the pump.  • Seal system- Special Plan52M  The system is used to provide a pressurized buffer fluid, at a lower pressure than the stuffing box to the space between the inboard and outboard seal of a 588USP cartridge.  As shown in Figure 5, this System uses a hydraulic accumulator to absorb any thermal expansion by the fluids in the seal loop and seal chamber. It also maintains a pressurized buffer fluid to serve as a reservoir to replenish seal leakage for a period of time if the make-up system is off line. The stored buffer fluid is piped to the local seal chamber circulation and cooling loops, where a pumping device is attached to the rotating element of the inboard seal. This pumping device circulates buffer fluid around the sealant system and the heat generated in the seal chamber by both the inboard and outboard seals is removed by this fluid circulation. It also ensures cooled liquid is available to be drawn into the spiral grooves, and removes any vapor or air present in the seal. Additional cooling   Copyright© 2018 by Turbomachinery Laboratory, Texas A&M Engineering Experiment Station is required for this application and a water cooler has been included in the scope to be installed into the seal chamber pipework.  The system is connected with site available demineralized water source, and the customer will ensure the water supply is continuous all the time. For upstream pumping technology, a stable, continuous liquid consumption source is critical. Generally all the sites have low temperature water utility.    Figure 5: Seal System for Upstream Seal (courtesy of John Crane)  Note: SG: Sight Glass; PSH- pressure switch High; PI-pressure indicator; PSL-pressure switch Low; F-flush port   Another key consideration on system design is sufficient cooling in order to bring the water circulation balance temperature down below 60 °C (140 °F). The reason for this is that the lubrication property of water becomes poor when the temperature is higher, which will impact outboard contacting seal. The other reason is to minimize the risk of scale forming in the water and depositing on the shallow spiral grooves of the inboard seal face, which could reduce pumping efficiency and cause the seal faces to contact and failure.  Most upstream pumping applications have the buffer fluid at atmospheric pressure or perhaps at a few meters head. But in this application case, because of the heat soak from the high process temperature, if the cooling system failed there was a risk that the buffer fluid could get hot enough to vaporize, which would lead to a reduced seal life. Therefore, the buffer fluid system is pressurized to a few bar, to ensure it stays liquid.  ADVANTAGE OF UPSTREAM PUMPING SOLUTION   Comparing the original and upgrade seal solution, there are several advantages as follows:  Firstly upstream pumping solution has been demonstrated to be more reliable and have longer MTBF (Mean-Time-Between-Failure) than single or even conventional dual seals on similar duties. The upgraded seal has run for at least 3 years in contrast to 1 year for the original seal. Upstream pumping uses non-contacting seal active lift technology; the stiff liquid film between sealing faces generates less heat than a normal contacting seal, and it is more tolerant of transient conditions that may occur in the equipment and process operation. Upstream pumping seal uses a low pressure water barrier (compared to a dual pressurized seal), this reduces the load on and heat generation of the outboard contacting seal, and ensures it runs well lubricated and under low stress, which extends the running life of the overall cartridge seal.  Secondly the upgraded solution has reduced the EHS (Environment, Health, and Safety) risk. Upstream pumping seal performs like a dual pressurized seal, so it’s “ZERO” emission solution. In addition, the acetic acid external flush was eliminated and water buffer is used, so the only leakage from the seal when running normally is water, not product.  Thirdly the initial cost and operating cost of the upgraded seal solution is lower than original one. In principle, the outboard seal can use normal stainless steel material as it is not wetted, whereas on the original seal all the metal parts had to be high grade anti-corrosion material. For this particular case, the special grade material was still used because of customer requirement. Also, the upstream pumping seal doesn’t need a continuous acetic acid flush, saving more cost.   Finally, more generally Upstream Pumping seals are a cost-effective alternative to both dual unpressurized and dual pressurized seals. While the initial cost of the seal and support system is broadly similar (it may be less in some circumstances), the payback is in the increased reliability and up-time of equipment, and reduction in routine maintenance time and effort that USP seals can offer.  CONCLUSIONS  Upstream pumping technology offers several advantages compared to conventional seal arrangements, especially for certain special applications. It offers increased reliability and reduced environmental impact. Its attractiveness is increased as it requires only a simple auxiliary system (fundamentally just a water supply) even though it offers it’s a more reliable seal performance.  Except for this case, upstream pumping products are also designed to provide reliable service in refineries, chemical/petrochemical processing, water treatment, mining, pulp & paper, and other industries where chemicals, low lubricity liquids, caustics, sour water, slurries and toxic products are pumped.   REFERENCES   Copyright© 2018 by Turbomachinery Laboratory, Texas A&M Engineering Experiment Station  International Programme on Chemical Safety (2010), Acetic Acid ICSC: 0363 [Online] 5 June 2010. Available at http://www.inchem.org/documents/icsc/icsc/eics0363.htm (Accessed 2017/9/16)  Centers for Disease Control and Prevention (1992), Occupational Safety and Health Guideline for Acetic Acid (Online). Available at https://www.cdc.gov/niosh/docs/81-123/pdfs/0002-rev.pdf (Accessed 2017/9/16)   API 682, 2014, “Pumps - Shaft Sealing Systems for Centrifugal and Rotary Pumps,” Fourth Edition, American Petroleum Institute, Washington, D.C. 

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Applying Upstream Pumping Sealing Technology for high corrosive fluid – Improve Reliability & Operating Cost

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Applying Upstream Pumping Sealing Technology for high corrosive fluid – Improve Reliability & Operating Cost

Abstract

Similar works

Full text

Available Versions

Texas A&M University

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