Vortex Pressure Reducing Station for Bulk CNG Appliations (VPRS-CNG)

Gasficient Consulting Services 1

Vortex Pressure Reduction Stations for Bulk CNG Applications

(VPRS-CNG)

An application of the innovative technology of

Prepared by: Gasficient Consulting Services

© 2012 Universal Vortex, Inc. All Rights Reserved. UVI logo is used with permission


General Requirement

• Bulk (non-vehicle) CNG for Distribution, Industrial or Off-Grid

• Typically Bulk CNG is Transported via truck and/or trailer at 250 barg

• CNG Pressure Reduction is required for utilization

• Typical capacities of 500 m3(s)/h, 1000 m3(s)/h, and 2000 m3(s)/h.


Overview of Typical CNG PRS Design

• Joule-Thomson effect is often compensated for by using a natural gas fired or electric boiler to pre-heat the gas

• Pressure reduction occurs using conventional pressure regulators often in 3 stages


Alternative Configuration: Vortex Pressure Reduction and Thermal Conditioning

• Pressure Reduction using VPR• Non-Freeze Pressure Reduction

Eliminates Pre-Heat • Thermal Conditioning after Pressure

Reduction by Warming the Cold Flow in Ambient Air Heat Exchangers


VPRS Basic Design

• Pre-heat is not required for vortex pressure reduction as the high pressure gas undergoes non-freeze pressure reduction in UVI’s proprietary self-heating vortex tube.

• After passing through the vortex tube the pressure reduced gas is warmed in a heat exchanger.

• The heat exchanger is warmed by a low grade heat source or often simply by ambient air.


Vortex Tube Maximal Flow

• Maximal flow is required for optimal mass & energy separation

• Flow through a vortex tube is maximal when flow becomes critical (choked flow) at some points in the vortex tubes.

• Maximal flow if the inlet:outlet pressure is ~2.2:1 or greater.

• Maximal flow rate is proportional to inlet pressure


Maximal Flow


Basic Configuration

• PR upstream of a VPR sensing and set for a specific VPR outlet pressure


Basic Configuration cont'd

• PR will regulate the inlet pressure to the VPR such that the flow will pass through the VPR to sustain the set downstream pressure

• When the required flow rate is high enough a 2.2:1 or greater pressure ratio will exist and maximal flow through VPR will exist.

• Multiple VPR function as one large unit so on/off control of units ensures maximal flow


Proposed VPRS-CNG Design

• Two stage vortex pressure reduction and thermal conditioning

• Single outlet VPR on the 1st Stage• Dual outlet VPR to enhance the available

natural gas thermal conditioning on the 2nd Stage.

• Pressure regulated VPR inlet concurrent with a Gas Management System resulting in efficient operation throughout the range of design pressures and flow rates.


Type of Vortex Pressure Reducer 1st Stage

• 1st Stage single stream outlet VPR (VPR-SS) for the 1st Stage as given the J-T cooling due to the large pressure reduction the combined flow at the VPR outlet will be sufficiently cold to capture significant heat from ambient air.

• After thermal conditioning, which largely compensates for 1st Stage J-T cooling, the pressure reduced gas enters the 2nd Stage.


Type of Vortex Pressure Reducer 2nd Stage

• 2nd Stage dual stream outlet VPR (VPR-DS) are used and after pressure reduction the cold stream if thermally conditioned before merging with the hot stream to provide a suitable temperature supply of gas to the Fine Tune Regulator.


Variable Pressure Regulated VPR Inlet

• The variable pressure regulated VPR inlet configuration provides control of VPR outlet pressure while varying the VPR inlet pressure.

• As the regulator responds to achieve the downstream pressure it increases or decreases the inlet pressure of the VPR

• VPR inlet pressure will vary as required to provide appropriate flow capacity to maintain the downstream pressure.


Gas Management System Control

• Using a GMS it is possible to select VPR runs in any sequence as required to match the cumulative VPR capacity with the required flow.

• Comprised of on/off solenoid valves, programmable logic controller (PLC), pressure and temperature transmitters


1st Stage VPR Runs

• Assuming the minimum size VPR has a capacity of 1 and the sizes of the other required VPR are expressed relative to this minimum size only 8 VPR (‘a’ through ‘h’) are required to provide VPR capacity as a multiple of the smallest VPR capacity

• Flexibility to adjust the total active VPR capacity it is possible to design a VPRS-CNG for highly variable design flow


2nd Stage VPR Runs

• For the 2nd Stage, due to the controlled inter-stage pressure, may require only 5 vortex tubes where Size 10 is sized for delivery of 10% of the design flow at the minimum stage operational pressure (eg 20 barg). Other 2nd Stage VPR have relative capacities as follows:


Heat Exchangers

• For ambient air a finned tube heat exchanger is recommended

• Gas temperature is warmed to within 5 degrees of the ambient air temperature as it flows through the heat exchanger

• Run switching with a second heat exchanger may be required for "defrost" of the passive unit since ice may build up due to otherwise continuous flow of sub-zero gas

• A small heater may be used to aid the melting


Previous Installations

• Approximately 40 installations of CNG VPR for Mobile units


Conclusion

• Questions & Discussion

Vortex Pressure Reducing Station for Bulk CNG Appliations (VPRS-CNG)

Design

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