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Recommendations and Guidelines DPC units are designed to be installed directly on a stable surface. Good quality soil fill should be used to build up to a non-flooding elevation. A gravel, crushed concrete, or caliche cap should be considered to stabilize the surface. The skid should be relatively level to insure proper operation: Two (2) inches maximum out of level along the long axis of the skid, and one (1) inch across the width of the skid. Do not allow the skid to be twisted by uneven support. This may put the equipment and piping in a bind and create undue stress on pressure retaining components. The greatest weight is under the heat exchanger support beams, and therefore the most benefit will be obtained by supporting these beams from the pad. Connecting Piping Connecting piping should be supported to keep loads on equipment nozzles and skid connections to less than 200 pounds, each. DPC maintains inlet and outlet gas flange connections on the same end of the skid to simplify unit size change outs. Inlet and Outlet Gas Connection Sizes:
Liquid dump lines from all skids are one inch screwed schedule 80 pipe. Electrical Classification The process skid has a Class I Group D Division 1 Electrical Area Classification due to the presence of instrument and power gas, which vents continuously. This must be considered when locating other electrical or flame fired equipment in the area of the skid to ensure safe operations. No smoking or any other open flames should be permitted in the immediate vicinity of the unit. THIS IS A HIGH PRESSURE NATURAL GAS CONDITIONING UNIT; THEREFORE ALL APPROPRIATE INDUSTRY AND COMPANY SAFETY PRECAUTIONS AND STANDARDS MUST BE ENFORCED. Unit Performance, Instrumentation and Controls Performance of the unit to achieve the specified dew point of the sales gas (cold separator temperature) is dependent on:
Be advised that a JT unit is sensitive to inlet gas temp. The performance guarantee for hydrocarbon dew point is only valid up to the maximum inlet temperature given to DPC when sizing the unit for the specific lease. If the inlet gas temperature rises above the design temperature, the sales gas dew point specification may not be achieved. Contact DPC if this occurs, or is anticipated to occur for assistance in troubleshooting the installation. The standard DPC JT unit is provided with a pressure controller to set the JT valve to the required upstream pressure. If the transporting pipeline varies widely in pressure, provision must be made to stabilize either the differential pressure across the skid/JT valve, or to stabilize the units outlet pressure. DPC provides a hot gas bypass and valve on the JT unit to assist in thawing the unit, or it can be used to reduce process temperature temporarily until pressure control can be stabilized. The DPC Mini JT unit was specifically engineered to operate in the 200 to 1,000 MSCFD range. Due to the small size, DPC worked hard to reduce the costs associated with this unit and thus the Mini JT does not have the same instrumentation as the larger DPC units. Contact DPC for assistance, if needed, on any of the above issues. Lessee is expected to provide proper overpressure safety system protection to prevent pressuring the DPC unit above 1440 psig. DPC provides an inlet gas safety relief valve connection for the Lessee’s use, if needed. The relief valve supplied by DPC is only designed for thermal relief protection. 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: When operating at cold separator temperatures of 35 degrees or higher:
When operating at cold separator temperatures 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. 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. 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. 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. 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 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:
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:
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