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Estudo de Caraterização e Melhoria de Desempenho da Fábrica de Água da Guia
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Resumo(s)
Uma ETAR apresenta um odor caraterístico devido à degradação da matéria orgânica
nas águas residuais. No caso particular da Guia, gerou-se algumas queixas de odores existentes
na ETFL, sendo que esta dissertação visa a identificação das possíveis causas e a sua resolução,
quer melhorando o sistema de desodorização quer otimizando o seu funcionamento.
Na tentativa de melhoria de desempenho, alterou-se as consignas do processo sendo
que se validou com as análises em GC/MS e GC/TCD ainda que não tenham sido observadas
alterações significativas. Efetuou-se um estudo da toxicidade dos compostos presentes nas
amostras, verificando-se que não há emissões prejudiciais para a atmosfera.
Com o objetivo de estudar o funcionamento do sistema e a possível melhoria com a
mudança de pratos para meio de enchimento aleatório simulou-se, em Aspen Plus e de uma
forma simplista, o cenário base que considera as três colunas de desodorização por lavagem
química, a coluna ácida, oxidante e básica, que removem os três principais compostos odoríficos
com concentrações de entrada de 30ppm em NH3, 20ppm em H2S e 3ppm em CH3SH para
um caudal nominal de 127 443kg/h. Realizou-se casos de estudo para diferentes caudais de
entrada de gás e distintas concentrações dos compostos odoríficos, onde se constatou que, à
saída do sistema, estes se situam com uma concentração de, no máximo, 1,239ppm em NH3,
0,0027ppm em H2S e 0,2245ppm em CH3SH sempre abaixo do valor limite de emissão para a
atmosfera, isto é, de 1,436, 0,072 e 1,712ppm respetivamente. No entanto, como o limiar olfativo
do NH3 é de 0,037ppm, do H2S é de 0,0005ppm e do CH3SH é de 0,0010ppm, é possível
sentir os seus cheiros caraterísticos. O grau de esgotamento dos reagentes das colunas de absorção
ronda os 46% para o ácido sulfúrico, 30% para o hipoclorito de sódio e 20% para a soda.
Para o enchimento obtém-se melhor eficiência quando comparado com uma média de 50%
dos pratos, eficiências de remoção superiores a 90% e menor queda de pressão de 0,00364bar
em vez de 0,081bar e ainda menor % de inundação da coluna, de 50% em comparação com
65%, para as mesmas condições de operação.
A WWTP has a characteristic odor due to the degradation of organic matter in the wastewater. In the particular case of Guia, there were some complaints about odors existing in the ETFL. This dissertation aims to identify the possible causes and their resolution, either by improving the deodorization system or by optimizing its operation. In an attempt to improve performance, the process guidelines were changed and it was validated with the analyzes in GC/TCD and GC/MS even though no significant changes were observed. A toxicity study of the compounds present in the samples was carried out, verifying that there are no harmful emissions into the atmosphere. To study the system functioning and the possible improvement due to the change of plates to random packing, the base scenario was simulated in Aspen Plus, in a simplistic way, which considers the three columns of deodorization by chemical washing, the acidic, oxidizing and basic column, which remove the three main odorous compounds with inlet concentrations of 30ppm in NH3, 20ppm in H2S and 3ppm in CH3SH for a nominal flow of 127 443kg/h. Case studies were carried out for different gas inlet flow rates and different concentrations of odoriferous compounds, where it was found that, at the exit of the system, they are located with a concentration of, at most, 1.239ppm in NH3, 0, 0027ppm in H2S and 0.2245ppm in CH3SH always below the limit value for emission to the atmosphere. That is, 1.436, 0.072 and 1.712ppm respectively. However, as the olfactory threshold of NH3 is 0.037ppm, H2S is 0.0005ppm and CH3SH is 0.0010ppm, it is possible to smell their characteristic scents. The rate of exploitation of the reagents in the absorption columns is around 46% for sulfuric acid, 30% for sodium hypochlorite and 20% for soda. For random packing, better efficiency is obtained when compared to an average of 50% of the plates, removal efficiencies are greater than 90% and lower pressure drops of to 0.00364bar instead of 0.081bar and even lower % of column flooding, 50% compared to 65% for the same operating conditions.
A WWTP has a characteristic odor due to the degradation of organic matter in the wastewater. In the particular case of Guia, there were some complaints about odors existing in the ETFL. This dissertation aims to identify the possible causes and their resolution, either by improving the deodorization system or by optimizing its operation. In an attempt to improve performance, the process guidelines were changed and it was validated with the analyzes in GC/TCD and GC/MS even though no significant changes were observed. A toxicity study of the compounds present in the samples was carried out, verifying that there are no harmful emissions into the atmosphere. To study the system functioning and the possible improvement due to the change of plates to random packing, the base scenario was simulated in Aspen Plus, in a simplistic way, which considers the three columns of deodorization by chemical washing, the acidic, oxidizing and basic column, which remove the three main odorous compounds with inlet concentrations of 30ppm in NH3, 20ppm in H2S and 3ppm in CH3SH for a nominal flow of 127 443kg/h. Case studies were carried out for different gas inlet flow rates and different concentrations of odoriferous compounds, where it was found that, at the exit of the system, they are located with a concentration of, at most, 1.239ppm in NH3, 0, 0027ppm in H2S and 0.2245ppm in CH3SH always below the limit value for emission to the atmosphere. That is, 1.436, 0.072 and 1.712ppm respectively. However, as the olfactory threshold of NH3 is 0.037ppm, H2S is 0.0005ppm and CH3SH is 0.0010ppm, it is possible to smell their characteristic scents. The rate of exploitation of the reagents in the absorption columns is around 46% for sulfuric acid, 30% for sodium hypochlorite and 20% for soda. For random packing, better efficiency is obtained when compared to an average of 50% of the plates, removal efficiencies are greater than 90% and lower pressure drops of to 0.00364bar instead of 0.081bar and even lower % of column flooding, 50% compared to 65% for the same operating conditions.
Descrição
Palavras-chave
ETAR Compostos odoríficos GC/MS GC/TCD Colunas de desodorização Aspen Plus