DPC uses a different refrigeration process than the typical propane model used in midstream. Our electric Freon units use off-the-shelf chillers that contain multiple independent circuits managed by an on-board PLC. The Freon package chills a water and ethylene glycol mixture to the temperature required for the process using 480V power provided by the client. The chilled water mixture is pumped to the process skid(s) and used to chill the gas to remove the hydrocarbons to meet pipeline specifications. DPC has different size chillers and process skids that can be mixed and matched to best meet a client’s needs.
The electrical chiller skids contain multiple independent circuits for extra reliability. The skid is controlled by an on-board PLC that manages circuit starting, balancing, and maintains the temperature set by the operator. It works very similar to your home or office thermostat and is almost as easy to operate.
DPC leases an all-electric refrigeration unit that was designed to meet the needs of the upstream production and midstream segments of the natural gas industry. These units have become very popular due to their ease of operation and installation, high turndown, and low operating costs. They have an operating range from 60° to –15 °F.
The refrigeration process skid consists of a gas-to-gas heat exchanger, a gas-to-chilled water heat exchanger, a two-phase separator, and an electrically pumped methanol distribution and injection system. The process skid is simple and very straightforward. Pumpers and gaugers find the unit very user-friendly, detracting little time from their routine production duties.
DPC refrigerates the gas by circulating a chilled water and ethylene glycol mixture. The chiller unit controls process temperature by precisely controlling the circulating water temperature. Each DPC chilled water unit operates with multiple compressors and a minimum of two isolated refrigeration circuits. A PLC controls the starting and loading of the multiple compressors and condenser fans. Each compressor loads in either 1/3 increments or by sliding vane or by variable frequency drive. The system includes a hot gas bypass, variable speed condenser fans and louvers for winter operation in cold climates. At extreme low load conditions, the entire chilled water unit will shut down and then self-start as needed. The unit has built-in phase and power outage protection and is set to self-start five minutes after continuous restoration of power after a clean power outage. All motor starters are included on the chilled water unit. The unit requires a single electric feeder drop with adequate overcurrent protection
DPC leases four standard sizes of refrigeration units:
- A2-R: 1 to 6 MMSCFD
- B2-R: 5 to 25 MMSCFD
- CB-R: 15 to 50 MMSCFD
- C2-R: 15 to 70 MMSCFD
Chilled water units are matched to the requirements of the refrigeration application. They all require 460 volt, three-phase, 60 hertz power. The following are standard DPC sizes and require the associated electrical service size and maximum overcurrent protection (actual power requirements are some 15% lower than the figures shown below).
|30 ton||75 amps||(100 KW generator)|
|50 ton||100 amps||(150 KW generator)|
|100 ton||250 amps||(250 KW generator)|
|150 ton||350 amps||(350 KW generator)|
|250 ton||700 amps||(600 KW generator)|
|330 ton||700 amps||(700 KW generator)|
The refrigeration process skids in the picture above have three heat exchangers. This plant was designed to handle hot gas downstream of a compressor discharge. The multiple heat exchanges reduce the chilled water unit size and lowers the overall expense of conditioning the gas stream. DPC supplies large hydrocarbon conditioning stations by operating multiple units in parallel. The pictures below show the installation of a 200 MMSCFD refrigeration plant at a pipeline station.
DPC’s refrigeration units are very similar to what is used on top of office buildings or next to schools. The units are safe to be used around offices, control rooms, property lines, or other public areas. On the other hand, it is non-classified equipment with open motors and must be placed at least 100 feet away from classified areas. API Code requires only 35 feet of separation however DPC believes that the risk of a low hanging NGL cloud and the open motors on the refrigeration unit require more caution. DPC generally recommends the units be placed wherever the power comes into the plant. DPC engineers can assist with site layout, contact us today.
The older chillers used in the DPC fleet use Freon R-22 refrigerant. All our technicians are licensed by the EPA and follow all regulations regarding Freon servicing including recapture, reporting, and leak detection and repair. Our newest chillers use the modern and safer R-134A and R-404A refrigerants.