Custom Wastewater Disposal Equipment & Solutions

Typical Dehydrator Operation

Oil and natural gas fields require electricity for several reasons. Among these are cathodic protection of the well casings and pipes, telemetry power, and lighting. If this power is not supplied by a connection to the grid, then it must be supplied from the field. The usual methods are to either provide small i.c. engine generator set, solar panels, or self-contained thermoelectric generator which is fueled with either propane or natural gas from the well. For the low-power requirements motor generator sets are expensive to operate and maintain, so that either solar or self-contained thermoelectric generators have been the solutions of choice. Solar panels have their advantages and disadvantages for these applications. One of the disadvantages of the stand-alone thermoelectric generator is that it can represent an additional combustion source within the field, and therefore it represents a potential safety hazard. Also since it burns potential sale gas it represents a further energy depletion. In addition, a stand-alone thermoelectric generator can be expensive. The alternative is to tap the sources of waste heat already available within the gas field.

One widely used existing source is the natural gas dehydrator system in which a liquid desiccant such as triethylene glycol is employed to remove moisture from natural gas. Gas extracted from a well is composed of a gaseous phase as well as distillate and water. Well-head gas and processing equipment is often situated at remote, relatively inaccessible locations and must be reliably continuously operable without attention by operating or maintenance personnel under variable and sometimes extreme climatic conditions. The well-head gas then must be transported, under pressure, great distances. Since well-head gas is usually at high pressure, the moisture, if not removed, tends to condense as the pressure is reduced upon entering the pipeline. This can lead to pipeline corrosion as well as the formation of water or ice within the distribution system subjecting the well producer to both expensive repair costs and loss of contracted sales gas.

A typical solution to the moisture problem is to pass the gas through a dehydrator to remove most of the water vapor and reduce the dew-point of the gas stream to a desired level for further handling or transportation of the gas. Gas dehydration is accomplished by passing the gas stream through an enclosure, including a pressure tower or vessel containing a series of stacked liquid desiccant membranes, where gas is brought into intimate contact with a stream of triethylene glycol. Water from the gas is absorbed in the triethylene glycol at 15 to 30°C. The absorbed water is subsequently removed from the triethylene glycol by circulating and heating the glycol/water solution to 175 to 200°C at atmospheric pressure. A gas-fired boiler, provides the source of heat to warm the glycol/water solution to separate and vaporize the water. The re-concentrated hot glycol is then cooled by means of well gas heat exchanger mechanisms and is returned to the contactor enclosure for absorption of moisture from further quantities of gas. The system is continuous in operation with the glycol circulation rate of 0.75 to 38 l/min depending on the capacity of the gas field.

Another clear source of available energy is the pilot light for the dehydrator heating system boiler. Heating systems such as these consist of an elongated burner housing containing a main gas burner unit, which is operable intermittently on demand when heat is required, and a pilot gas burner unit which provides a continuous flame to ignite the main burner unit. The pilot burner has a thermal output of 29 kilowatts.

The boiler emissions stack is also a considerable source of available energy to convert into electricity. The energy from the hot combustion gasses leaving the dehydrator boiler can be from 66 kilowatt to over 293 kilowatt. The temperature of the stack gas can vary over a wide range depending on boiler rating and whether only the pilot is burning or both the pilot and main burner are in operation.

The dehydrator system represents a potential source of energy recovery for conversion into electricity. All three systems described produce a large amount of waste heat which we can utilize for our generators. These types of applications are typical of daily and yearly operation. We can provide the oil & gas producer a unique option to provide power for todayÕs innovative components to insure consistent uninterrupted revenue of sales gas.