Pilot Test and Economic Analysis of a Wellhead Produced Water Purification System Based on Humidification and Dehumidification Using Co-Produced, Solar, and Waste Heat

Abstract

Abstract This paper presents field testing results and economics analysis at pilot scale for a humidification- dehumidification (HDH) process, described in SPE 169526, and to demonstrate that the process is viable and cost-effective, using solar, latent geothermal, and waste heat to augment the process for continuous operation. The HDH process drops produced water heated to 145–185°,F down chambers with up-blowing ambient air which humidifies the air at elevated temperatures to relative humidity >99%. The water- laden air then drops into adjacent cooling chambers and fresh water condenses out. Additional fresh water yield is achieved by using a secondary air-cooled condenser. To accomplish pilot test goals, a field scale prototype was constructed and tested at a field test site near Artesia, New Mexico, to determine operational parameters with solar heating, and then at the Federal 00 well in Eddy County, New Mexico, an oil well that produces ~20 BBLs of water per day, to test unattended operation and economics. The HDH unit was sized for the Federal 00's water production and can process 51 BBls of produced water per day. The field setup utilizes latent geothermal heat in the produced and heat is added to the water using an array of 16 flat plate solar panels. Heated water passes into an insulated storage vessel, which then feeds the HDH unit. When the solar panels are not generating heat, produced water is fed directly into the heated storage. At night or on cloudy days, additional heat can be supplied to the storage tank by burning waste gas. An Arduino controller manages the process flow, switches fluid flow as needed, and monitors tank levels. The HDH unit can purify ~20% of the inlet water on each pass, and the outlet concentrate, at ~125°F, can be cycled back into the hot water storage tank. The system was tested in summer and winter conditions. Winter conditions have drier inlet air, but less solar energy, and conversely summer has wetter inlet air, but more available solar heating. Summer tests yielded ~8-9 BBLs per day of purified water, and winter tests produced ~11 BBLs per day, for an annualized average of 10 BBLs per day, potentially cutting the disposal needed for the Federal 00 in half. Purification costs are primarily from electrical use of small pumps, a blower, and an air-cooled condenser. These average $3.82 per day, corresponding to ~$0.55 per barrel in summer and ~$0.35 per barrel in winter to purify water. Cost offsets from selling the fresh water and reduced disposal costs yielded an 85% reduction in annualized produced water handling costs.