Inlet Moisture Considerations | Startup Assistance & Field Service | Pressure Storage & Facilities Design & Procurement Statement

Inlet Moisture Considerations

Inlet gas moisture (water) content control is required to maintain continuous operation of the gas conditioning process. It is crucial that only a properly dehydrated inlet gas be fed to the skid inlet to avoid ice and hydrate problems.

Dew Point Control recommends the following precautions to help prevent hydrate and ice formation:

  1. When operating at cold separator temperatures of 35 degrees or higher:
    • Dehydrated gas fed to the DPC unit should have no more than 7#/MMSCF of water content.
    • Methanol injection is not normally needed with a properly operating glycol unit, although it is recommended that methanol be injected for one shift per week to keep the system “clean.”

  2. When operating at cold separator temperatures below 35 degrees:
    • Dehydrated gas fed to the DPC unit should have no more than 3#/MMSCF water content, requiring, in most cases, stripping gas on the re-concentrator reboiler, an eight tray contactor, and a reboiler temperature of no less than 385 degrees.
    • Methanol injection is recommended to keep unit clear of hydrates and ice when operating below 35 degrees.
    • When the unit chills the gas to the vicinity of hydrate formation or ice formation temperature, methanol must be injected using the DPC provided on-skid pump. When using DPC’s high efficiency methanol injection system, methanol flow should be set at 2.5 pounds of methanol per pound of inlet water by setting the strokes per minute of the injection pump. (1.2 gallons of methanol per MMSCF of 3# gas)
    • Because of the potential for a freeze blockage in the unit, it is strongly recommended that a pressure controlled unit bypass be installed across the inlet and outlet piping to permit continuous gas delivery to the pipeline until skid operation can be restored to normal. If the pipeline will not permit offspec gas to flow for startup or thawing, or other system troubleshooting, then provision should be made to safely dispose of the off-spec gas during these periods, such as a flare or vent stack located safely at the edge of the facility and away from any exposure to neighboring personnel, residents, houses, businesses, etc.

DPC will work with the Lessee to recommend or provide additional controls and devices to meet specific or unique requirement for any location.

Startup Assistance and Field Service:

Standard DPC field service included in the rental rate includes up to two days initial onsite startup assistance, quarterly jobsite visits/consultations, and telephone and email support for troubleshooting and assistance. Additional onsite service is available on a Time and Material reimbursement basis. In addition, our Instrument/Electrical contractor is available for any onsite work, on our equipment or other, on a case-by-case basis negotiated and priced directly with the contractor.

  1. Operator Maintenance Responsibilities

    • Lessee is expected to maintain the unit properly, including safeguarding the inlet from various contaminants that will materially interfere with the proper operation of the equipment. Lessee is required to properly clean the unit at the end of the lease prior to returning it to the DPC yard, otherwise a cleaning fee will be imposed. As part of the DPC field service, DPC will coordinate with lessee to inspect the unit prior to leaving the lease; this should alleviate any additional cleaning fees. It is especially important for both safety and regualatory reasons, that ALL liquid hydrocarbons be blown down and removed from the units prior to loading on truck transport.
    • DPC shall transfer to Lessee any warranties made to DPC by the manufacturer or supplier. Specifically, instrumentation items and chemical injection pumps will be repaired and maintained during the initial 30 day operating period, while the remaining equipment and piping will be repaired or rebuilt by DPC during the entire term of the lease. Normal and routine equipment and instrument maintenance, such as cleaning, and clearing of debris from valves or other equipment, or tightening of flange, threaded joint, or packing gland or stuffing box leaks, will be the responsibility of the Lessee.
    • In general, DPC expects that the Lessee will operate, troubleshoot, and maintain the process skids, or any other equipment, besides the chilled water packages, as if they were their own.

  2. Operational Issues and Troubleshooting
    Sales Gas Dew Point or Unit Freeze-up Problems:

    • The biggest operational issue that DPC encounters with the operation of JT units is the fluctuation of the sale pipeline operating pressures. The DPC JT unit is instrumented to hold a constant pressure upstream of the unit. When the sales pipeline varies in pressure, this changes the differential pressure across the JT value, which causes wide variations in the process temperatures. The hydrocarbon dew point at the operating pressure of the unit is the temperature of the cold separator. Fluctuating temperatures will cause fluctuating dew point temperatures. When the process temperature gets too cold, the unit can freeze or hydrate. The simplest and most reliable fix for varying pipeline pressure is to install a backpressure controller and valve downstream of the unit. Set this controller at approximately 30 psig above the highest-pressure swing expected on the pipeline. This will stabilize both the pressure drop across the JT valve the unit operating temperature.
    • The JT skid hot gas bypass valve (the one that has a manual regulator) can also be automated with a KimRay T-12 temperature controller. This gas bypass can control temperatures over a range of approximately 15 degrees. A thermowell is provided on the unit, on the exchanger nozzle feeding gas to the separator, to permit field installation of the temperature controller.
    • The manual hot gas bypass is used when icing or hydrate problems are suspected. Opening the bypass will warm up the unit approximately 15 degrees. This is an easy solution that does not affect any instrument settings or operating pressures.

Pressure Storage and Facilities Design and Procurement Statement

DPC offers, on a lease basis, pressurized storage tanks, as a service to customers who lease DPC JT or refrigeration natural gas conditioning equipment. The tanks are nominally 18,000 gallon, 250 psig rated ASME pressure vessels, skid mounted, and suitable for truck tailgate loading and unloading when completely empty. This service is offered only to allow producers who are in a schedule bind, time to find and provide their own tankage at a more leisurely pace.

Pressure storage tanks are leased under the following option:

Provision of a “bare” skid mounted pressurized storage tank as described above, FOB our shop near Houston. This is a straight non-service supported lease item, and it is up to the lessee to provide installation, dress out of the tank with appropriate and legal appurtenances (valves, including reliefs, etc.) and to install per good engineering practice and all rules and regulations of the appropriate authorities. In addition, the lessee will need to install the correct and appropriate truck loading facilities, including safety systems, as required by federal, state and in some cases, local authorities. These may include, but are not limited to: DOT, EPA, Texas Railroad Commission, and State and Local Fire Marshals.

For dressing of the tank with appropriate devices and the installation materials and labor required by the lessee’s Facility Engineer or Contractor, we recommend the services of:

ProCon Construction, Inc

2875 Woods Road 

Brookshire, Texas 77423
Contact: Royce Reid 

Phone: (281) 375-6829

Fax: (281) 375-5644

Email: [email protected]

Please note that Dew Point Control, LLC is not set up or staffed to be a provider of facility or other engineering services nor of material procurement assistance. Advice and counsel are freely given as they relate to the facilities that we lease, but facilities and site engineering should be sought from appropriate companies in that business. DPC will be glad to recommend such firms upon request.

Should lessee elect to dress the tank(s) and provide installation materials to it’s contractor and/or lease crews, DPC recommends that you contact experts in the field of LPG storage and handling equipment who can recommend and supply the correct material and installation advice, such as:

Gas Equipment Company 

11510 N. Petropark

Houston, Texas 77041
Contacts: Jerry Drake or Jarrod Griffin
Phone: (713) 896-1077
Fax: (713) 896-9299
Email: [email protected] or [email protected]