Conversion of N-containing compounds of flash steam condensate from carbamide production into hydrazine sulfate

Abstract

Formation of 1.5 m³ of wastewater per 1 ton of carbamide in the form of flash steam condensate accompanies carbamide production. It is necessary to purify flash steam condensate from nitrogen compounds by two-stage desorption and hydrolysis. Disposal of residual N-containing compounds occurs at biological wastewater treatment plants under industrial conditions. Such a multistep purifying method leads to reduction of up to 72–77 % of N-containing compounds, but it requires high electrical and thermal energy costs. The method is the most modern and the most promising one, it is implemented at carbamide synthesis plants everywhere.

The study proposes a new method for the disposal of N-containing compounds in flash steam condensate produced by carbamide production by processing ammonia, carbamide and biuret to hydrazine sulfate. The study on the synthesis of hydrazine sulfate in wastewater from the production of carbamide defined mechanisms occurring during synthesis of raw hydrazine in an electromagnetic reactor. The study proved that the proposed method of disposal is economically viable, environmentally friendly and energy efficient. It reduces a load on biological wastewater treatment plants, reduces the cost of electrical and thermal energy.

The method gives a possibility to process N-containing compounds of flash steam condensate into an expensive product ‒ hydrazine sulfate. Experimental studies confirmed that electromagnetic radiation has a positive effect on the synthesis of raw hydrazine. This leads to an increase in efficiency of the hydrazine synthesis reactor by 88 %. We analyzed three of the most probable chemistries of the process of raw hydrazine synthesis reactions using the non-imperial method of quantum chemistry. The study showed that the initial yield of the finished product is 5.3 kg per 1 m³ of nitrogen-containing raw materials during disposal of flash steam condensate at a model plant by processing into hydrazine sulfate taking into account an optimization parameter. There is an increase in the yield of the final product to 6 kg per 1 m³ at repeated multiple use of the filtrate as a source of sulfuric acid. We performed a projection of the results of the model installation at industrial scale taking into account an operation of the carbamide synthesis device, with a capacity of 330,000 tons/year. Thus, we identified that the maximum estimated production capacity of the hydrazine sulfate synthesis unit is 132–150 kg/day. We calculated the profitability of the device for the synthesis of hydrazine sulfate considering the obtained data on the estimated capacity of the device. We established that the net profit is at least 12 % according to the proposed scheme in the production of hydrazine sulfate