Drag reducing cationic surfactant solutions for district heating and cooling systems.

摘要

Pumping energy costs are a major operating cost in closed loop district heating and district cooling systems. The use of non-degradable cationic surfactant drag reducing additives to reduce the pumping energy requirements, to increase water throughput, or to reduce pump size or pipeline diameter is potentially attractive. Drag reduction for cationic surfactant solutions (quaternary ammonium salts with one long alkyl group and aromatic counter-ion) in circulation flow systems has been extensively investigated. The effective temperature range in which drag reduction occurs was found to be affected by factors such as chemical structure of surfactant and counter-ion, concentration of surfactant and counter-ion, solution pH, preshearing, pipe diameter, and other additives such as corrosion inhibitors.;Drag reduction at high temperatures can be obtained by using long chain surfactants. Drag reduction at low temperatures can be enhanced by incorporating one or more double bonds into the surfactant chain or by replacing the methyl groups on the surfactant headgroup with hydroxyethyl groups. The use of mixed surfactants or mixed counter-ions can also reduce the lower temperature limit.;Aromatic counter-ions such as derivatives of benzoate, benzenesulfonate, or naphthoate are more effective in inducing drag reduction than inorganic ions. Good drag reduction can be obtained if the hydrophilic and hydrophobic substituent groups are located on the opposite sides of the phenyl ring.;A scale-up method based on Virk's three-velocity-zone model was found to give good predictions in going from the 0.106-inch tube to the 0.243-inch tube. The results of a field test performed in a 6-inch pipe circulating heating system at Argonne National Laboratory demonstrate the feasibility of using surfactant drag reducers in commercial pipelines.;After a few days of continuous shearing, drag reduction is lost, presumably due to interactions of the surfactant with dissolved oxygen and system metal parts. The loss of effectiveness can be compensated for by adding passivator-type corrosion inhibitors or by using higher concentrations of surfactant.