Stublach Gas Storage

Storengy UK is currently developing the Stublach Gas Storage Project, a salt cavern storage facility in Cheshire. Once completed, the scheme will be one of the main storage facilities in the country, and will enhance the security of supply to the UK market.
 

Supplying oil and gas equipment for Storengy and Jacobs Engineering

Project Info

End user

Storengy UK ltd.

Contractor

Jacobs Engineering U.K.

Location

Stublach, Northwich, Cheshire, UK

Year of Supply

2013

Gas dehydration trains, slug catchers, shell and tube heat exchangers and more

Twenty caverns will be created in total, the first two of which will go online in 2014. The remaining cavities are expected to be fully developed by 2018.
 
Storengy UK will operate the first 40 million cubic meters of natural gas in 2014, and by 2018 the total storage capacity could reach 400 million cubic meters.
 
Thanks to very high injection and withdrawal rates – up to 30 million cubic meters per day – the store benefits from flexible services, along with fast-cycling products, allowing users to churn gas many times during the year.
 
Frames was invited to supply the gas treatment facilities for the  gas storage project. The delivery included the gas dehydration trains,  interconnecting piping, the glycol regeneration units and the hot water boiler system. The dehydration trains will reduce the water content in the natural gas to less than 30ppm to reach the gas specification required for the gas transmission.
 
Gas from the underground gas storage facility is fed to the slug catcher, where free liquids present in the gas are removed. To prevent hydrate formation, the gas temperature is then increased in the gas heaters to a minimum of 16 °C before entering the dehydration towers. For this purpose, hot water is supplied by the hot water heating package. In the dehydration tower, wet gas is dried by flowing counter current against dry TEG (tri-ethylene-glycol) over a structured packing.
 
The glycol regeneration units are used to regenerate wet TEG into dry TEG by separating (absorbed) water and dissolved hydrocarbons. Wet TEG is dried in the reboilers, where it is heated to a temperature of 204 °C by means of a heating coil with flue gas from the economizer.

Our approach to gas treatment

One of the challenges of this project was the transportation to the site, which called for a particular Frames service: modular construction for easy transportation and quick assembly on site. In total, the project consisted of twelve modules and four towers. Through extensive collaboration between Storengy and Frames' engineers, the project team managed to split the modules into nineteen transportable packages. The modules were shipped to the site, where they were reassembled under the supervision of Frames' construction engineers. 

Stublach Gas Storage scope of supply

  • 2x gas dehydration trains comprising the following:
    • Slug catcher with integrated inlet separator
    • Dehydration tower
    • Filter skid with high-pressure TEG filters
    • Heat exchanger skid with shell and tube heat exchangers
    • 20" Interconnecting piping
  • 3x glycol regeneration units, with TEG reboiler and economizer (OVC)
  • Pump skid with 3 high-pressure TEG pumps (1 spare)
  • Hot water heating package, with two gas-fired 2.8 MW boilers
Technical Details
  • Gas dehydration trains:
  • Gas flow rate: 8.25 MMNm³/day/train
  • Glycol type: TEG
  • Design pressure: 98 barg
  • Regenerator type: OVC
  • Operating temperature: 16-40ºC
  • Inlet water content: 700 mg/Nm3
  • Outlet water content: <30 mg/Nm3
Slug catcher
The wet gas is fed to the slug catcher to remove any free liquids present from the gas flow before it enters the gas heater and dehydration tower for further treatment.
The slug catcher consists of a vertical separator with vane-type inlet device, a vane-type outlet device + demister with an efficiency of removal of 99% of droplets of 10 microns and larger.
 
Gas Heater skid with shell & tube heat exchangers
The wet natural gas from the slug catcher is fed to the tube side of gas heater before entering the dehydration tower. The purpose of the gas heater is to heat the gas from approximately 9 °C to at least 16 °C to prevent hydrate formation. The heating medium flows through the shell side of the gas heater to heat up the wet gas. The gas heater is a TEMA type: BEM (VEV) with the heads welded to the tube sheet.
 
Dehydration tower
The dehydration tower functions as a scrubber, and is equipped with various internal – e.g. structured – packing. Its purpose is to reduce the water content of the natural gas to a desired dew point.
The design takes into account a height limitation of 10m above grade, enabling it to stay below the requested 10 meters, with the outlet nozzle positioned on the side of the tower.
The dehydration tower is equipped with the follow internals:
  • Frames Advanced Vane-type Inlet Device (FAVID)
  • Structured gas dehydration packing (incl. distributor)
  • Wire mesh demister
Filter skid with high pressure TEG filters
High-pressure (HP) TEG filters are designed to remove suspended solids and particles from the wet TEG liquid flow before it enters the downstream equipment, e.g. wet TEG tank.
 
Glycol Regeneration units, with TEG Reboiler and Economiser (OVC)
The regeneration units have been designed to regenerate wet tri-ethylene glycol (TEG) liquid into dry TEG liquid, and consist of the following:
  • Glycol  Regeneration Unit
    • TEG Filters
    • Reflux Condenser
    • Still Column
    • Reboiler
    • Stripping Column
    • Dry TEG Surge Drum
    • Dry TEG Transfer Pumps
    • TEG/TEG Heat Exchangers
  • OVC Unit
    • Economiser
    • Stack
    • Flue Gas Fan
    • Combustion Air Fan
    • Burner management system (BMS) economiser

Pump skid with  High Pressure TEG pumps
The purpose of the high-pressure TEG pump is to route dry TEG liquid from the dry TEG tanks to the top of dehydration tower. The high-pressure TEG pump skid is equipped with one dedicated pump per corresponding dehydration tower, and a shared spare pump. The high-pressure TEG pumps will increase the pressure of the dry TEG in the operating range between 40-85 barg.
 
Hot Water Heating Package, with two gas fired 2.8 MW Boilers
To provide the heat for the Gas Heater, a hot water heating package was installed consisting of:

  • Hot Water Heater
  • Coupling Vessel Expansion Vessel
  • Coupling Vessel Intermediate Vessel
  • Coupling Vessel
  • Heater Recirculation Pump
  • Hot Water Heater Stack
  • Hot Water Circulation Pump
  • Coupling Vessel Expansion Vessel
  • Coupling Vessel Intermediate Vessel
  • Make-up Pump
  • Hot Water Heating Package Control Panel
  • Rated output 2.8Mw
  • Volume 5.6 m3
  • Operation temperature 950C
  • Operation Pressure 4 Barg

Client’s Key Benefits

  • Tailor-made equipment designed and engineered for maximum withdrawal from the caverns.
  • Modular construction for easy transportation and quick assembly on site.
  • Fast commissioning and start-up.
  • Engineered for easy future expansion.