A Highly Efficient Waste-Free Technology of Water and Fuel Preparation for Thermal Power Stations

Abstract

A highly efficient, economical, and waste-free technology for the purification of natural waters for thermal power plants has been developed. The preliminary purification of water involved microfiltration on tubular ceramic membranes made of clay minerals according to a technology developed at the Dumansky Institute of Colloid Chemistry and Water Chemistry, NAS of Ukraine; the degree of retention of suspended solids and iron and manganese compounds on the membranes was 99.9, 99.8, and 60%, respectively. The high separation capacity of such membranes is due to the modification of their surface by water contaminants with the formation of a self-organizing dynamic membrane that serves as an additional barrier. The dynamic membrane formation contributed to the retention of up to 24.0% of the co-occurring ions, Ca²⁺ in particular; this is typical for ultrafiltration membranes. Further desalination was performed with low-pressure reverse osmosis membranes; two stages of reverse osmosis turned out necessary to achieve a total ion content of 0.5 mg/dm³ in the make-up water of a steam turbine unit of a thermal power plant (TPP). The retentate of the second stage of reverse osmosis, for which the total ion content is 50–60 mg/dm³, can be used for technical purposes at TPPs. The salt content of the retentate formed after the first stage of reverse osmosis was ~3 g/dm³, and thus insufficient for further transformation into secondary material resources; however, the introduction of waste recycling systems is considered to be the modern direction in protecting the environment from technological influence. The retentate of the first stage of reverse osmosis was concentrated using an original concentrating electrodialyzer developed at the Dumansky Institute of Colloid Chemistry and Water Chemistry, NAS of Ukraine; some design modifications that distinguish this electrodialyzer from the conventional ones were proposed and patented. Electrodialysis treatment of the retentate for 2.5 hours at a current density of 2.5 A/dm³ enabled the production of a solution with the ion content of ~105 g/dm³. This brine can be converted into sodium hypochlorite or caustic soda and hydrochloric acid by electrolysis. The diluate with a mineralization of ~200.5 g/dm³ and a total organic carbon content of ~148.3 g/dm³ can be used for the preparation of coal-water slurry fuels for power generation and metallurgy. The basic technological schemes of make-up water purification for the needs of thermal power plants and the preparation of slurry fuel systems based on coal and reverse osmosis waste that contains organic substances are proposed.