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Reciclagem das purgas amoniacais das fábricas de ácido nítrico na produção de amónia
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Abstract(s)
O presente trabalho surgiu da necessidade ambiental de tratar o efluente amoniacal produzido pelas fábricas de ácido nítrico por meio da purga dos evaporadores e reaproveitá-lo para uma futura produção de solução amoniacal pura. Deste modo, para evitar o tratamento deste efluente, foi construída uma instalação de filtração para reaproveitar a solução amoniacal de modo a poder incorporada na produção de amónia (solução amoniacal a 24,5%).
Assim, a realização deste trabalho visa a otimizar e propor melhorias para a instalação de filtração, tendo em vista um tratamento mais eficiente do efluente. Este trabalho foi realizado em duas fases, sendo a fase 1, a fase de análise do comportamento da solução amoniacal impura após a filtração tendo-se variado o caudal, a concentração e o resíduo seco. Nesta fase, o resíduo seco foi determinado pelo método de evaporação. Na fase 2, realizou-se mais de uma mais de uma passagem das soluções amoniacais e foram realizadas análises à concentração da solução foi utilizado o método de evaporação e extração com solvente tetracloroetileno para a determinação do teor óleo e resíduo seco.
Inicialmente, foram realizados estudos à concentração da solução amoniacal impura, através do método de titulação com acido sulfúrico 0,9975M. Como a especificação da solução amoniacal é 24,5% de amoníaco, à concentração da solução a filtrar vai ser colocada dentro da especificação depois de filtrada e posteriormente incorporada na produção da solução amoniacal pura, não sendo de especial relevo a concentração inicial. Seguidamente, foram realizados ensaios de filtração com apenas uma passagem e caracterizados por gravimetria através da evaporação da solução amoniacal impura para determinar a concentração de resíduo seco. Nestes ensaios verificou-se que à medida que o caudal aumentava, aumentava a quantidade de resíduo da amostra filtrada, ou seja, maior resíduo seco na amostra final. Para valores 8,5 dm3/min os teores de resíduo seco foram relativamente baixos, para valores superiores 10,5 dm3/min a concentração de resíduo seco aumentava exponencialmente. Definiu-se assim que os valores de caudal para os estudos posteriores fossem sempre iguais ou inferiores a 8,5 dm3/min.
Seguidamente, foram realizados ensaios com mais de que uma passagem através da instalação de filtração. Nestes ensaios observaram-se uma redução da concentração de óleo até 0 mg/kg. No entanto, essa redução não foi suficiente para atingir os valores pretendidos no que se refere ao resíduo seco. O resíduo seco total continuou a ser superior a 10 mg/kg amónia, valor da especificação. Contudo verificou-se que mais duas passagens seriam suficientes para atingir valor adequado para ser integrado na produção da solução amoniacal pura.
The present work arose from the environmental need to treat the ammoniacal effluent produced by the nitric acid plants due to the evaporators purges in order to reuse them for a future production of pure ammoniacal solution. To avoid the treatment of this effluent, a filtration facility was built to reuse the ammoniacal solution in order to be incorporated in the production of ammonia (24.5 wt. % ammoniacal solution). Thus, this work aims to optimize and propose improvements for the filtration plant, leading to a more efficient treatment of the effluent. The work was carried out in two phases. In phase 1 the analysis of the behavior of the impure ammoniacal solution after filtration, varying the flow rate, the concentration and the dry residue was undergone. In this phase, the dry residue was determined by the evaporation method. In phase 2, more than one pass of the ammonia solutions was carried out, and analysis to the solution concentration were carried out. The evaporation and extraction methods with tetrachlorethylene solvent were used to determine the oil and dry residue content. Initially, studies on the concentration of the impure ammoniacal solution through titration with 0.9975M sulfuric acid were carried out. It should be noted that the concentration of the solution to be filtered will be placed within the specification after it is filtered and later incorporated into the production of the pure ammoniacal solution, not being an issue of special importance. One-pass filtration tests were performed and characterized by gravimetry through the evaporation of the impure ammoniacal solution to determine the dry residue concentration. In these tests it was found that as the flow increases, the amount of residue in the filtered sample increases, that is, higher dry residue in the final sample. For flow rates up to 8.5 dm3/min, it was found that the dry residue levels were relatively low. For values above 10.5 dm3/min, the dry residue concentration increased exponentially. Thus, for phase 2 studies, 8.5 dm3/min or lower flow rates were used. Tests were then carried out with more than one pass through the filtration installation. In these tests, improvements were observed with the reduction of the oil concentration to 0 mg/kg. However, this reduction was not enough to achieve the desired dry residue values. The total dry residue remained greater than 10 mg/kg ammonia, in a value of the specification. However, it was found that two passes would be enough to reach a suitable value to be integrated in the production of the pure ammoniacal solution.
The present work arose from the environmental need to treat the ammoniacal effluent produced by the nitric acid plants due to the evaporators purges in order to reuse them for a future production of pure ammoniacal solution. To avoid the treatment of this effluent, a filtration facility was built to reuse the ammoniacal solution in order to be incorporated in the production of ammonia (24.5 wt. % ammoniacal solution). Thus, this work aims to optimize and propose improvements for the filtration plant, leading to a more efficient treatment of the effluent. The work was carried out in two phases. In phase 1 the analysis of the behavior of the impure ammoniacal solution after filtration, varying the flow rate, the concentration and the dry residue was undergone. In this phase, the dry residue was determined by the evaporation method. In phase 2, more than one pass of the ammonia solutions was carried out, and analysis to the solution concentration were carried out. The evaporation and extraction methods with tetrachlorethylene solvent were used to determine the oil and dry residue content. Initially, studies on the concentration of the impure ammoniacal solution through titration with 0.9975M sulfuric acid were carried out. It should be noted that the concentration of the solution to be filtered will be placed within the specification after it is filtered and later incorporated into the production of the pure ammoniacal solution, not being an issue of special importance. One-pass filtration tests were performed and characterized by gravimetry through the evaporation of the impure ammoniacal solution to determine the dry residue concentration. In these tests it was found that as the flow increases, the amount of residue in the filtered sample increases, that is, higher dry residue in the final sample. For flow rates up to 8.5 dm3/min, it was found that the dry residue levels were relatively low. For values above 10.5 dm3/min, the dry residue concentration increased exponentially. Thus, for phase 2 studies, 8.5 dm3/min or lower flow rates were used. Tests were then carried out with more than one pass through the filtration installation. In these tests, improvements were observed with the reduction of the oil concentration to 0 mg/kg. However, this reduction was not enough to achieve the desired dry residue values. The total dry residue remained greater than 10 mg/kg ammonia, in a value of the specification. However, it was found that two passes would be enough to reach a suitable value to be integrated in the production of the pure ammoniacal solution.
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Keywords
Solução amoniacal Reaproveitamento Filtração Óleo Resíduos Ammonia solution Reuse Filtration Oil Waste