Case Study #6 – Liquid Nitrogen for Natural Gas Dilution

Company:

This major electric and gas utility company includes businesses of regulated electric and natural gas utility operations and other non-regulated energy-related businesses. Two sites are located in the Southeastern part of the U.S.

Design Challenges:

  • Dilute incoming natural gas feed stock by 2.5% with nitrogen to control BTU quality
  • Design and verify LN2 for 2.5% of volume
  • Four days of LN2 on-site storage at 24 hours/day operation
  • Design surge capacity in pipe downstream of vaporizers to minimize on/off cycling of pumps

Solution:

Install three 30,000 gallon storage vessels for a total of 90,000 gallons of LN2 storage at Site A and four 15,000 gallon storage vessels for a total of 60,000 gallons of LN2 storage at Site B.*

 

The pump skid is specifically engineered to provide optimum performance with the Chart Siphon 100® Bulk Storage Tank design. The skid is self-contained, pre-assembled, and tested to meet specification requirements. The pump skid takes low pressure liquid nitrogen from the Siphon 100 tank, increases the pressure, and force-feeds the vaporizers and downstream piping to the gas injector system.

 

*Each site to use one pump skid, four ambient vaporizers, and one nitrogen gas injector.

 


Design basis specific to Site A includes:

  • Requirements to dilute the LNG require nitrogen injection at the rate of 82,000 SCFH, equating to 16.4 GPM pumping and on-site storage of 93,000 gallons of LN2 to meet the 4 days at 24 hours/day operation.
  • 10” pipe tie-in
  • GE PLC control system
  • Additional flow meter required downstream of injector (use as a check meter) and must be compliant with applicable AGA custody transfer standards.

 


Design basis specific to Site B includes:

  • Requirements to dilute the LNG require nitrogen injection at the rate of 55,000 SCFH, equating to 10.8 GPM pumping and on-site storage of 60,000 gallons of LN2 to meet the 4 days at 24 hours/day operation.
  • 8” pipe tie-in
  • Bristol control system
  • Meter is an orifice style, must be compliant with applicable AGA custody transfer standards
  • Instrument air circuit required at 100 – 115 psi

 

Outcome:

Successful economic dilution of incoming natural gas feed stock by 2.5% with nitrogen gas from LN2 storage.