Title: Exergy and environmental analysis of black liquor upgrading gasification in an integrated kraft pulp and ammonia production plant

Authors: Meire Ellen Gorete Ribeiro Domingos; Daniel Flórez-Orrego; Moisés Teles Dos Santos; Hector Ivan Velásquez; Silvio De Oliveira Junior

Addresses: Department of Chemical Engineering, Polytechnic School, University of Sao Paulo, Av. Prof. Lineu Prestes, #580, 05508-000 São Paulo, SP, Brazil ' Department of Mechanical Engineering, Polytechnic School, University of Sao Paulo, Av. Prof. Mello Moraes, 2231, 05508-030 São Paulo, SP, Brazil; Faculty of Minas, National University of Colombia, Av. 80 #65, 223, Medellín, Colombia ' Department of Chemical Engineering, Polytechnic School, University of Sao Paulo, Av. Prof. Lineu Prestes, #580, 05508-000 São Paulo, SP, Brazil ' Faculty of Minas, National University of Colombia, Av. 80 #65, 223, Medellín, Colombia ' Department of Mechanical Engineering, Polytechnic School, University of Sao Paulo, Av. Prof. Mello Moraes, 2231, 05508-030 São Paulo, SP, Brazil

Abstract: The black liquor is a byproduct of the kraft pulping process that contains more than half of the exergy content in the total woody biomass fed to the digester, representing a key supply of renewable energy to the pulping process. In this work, the conventional scenario of the black liquor use (i.e., concentration and combustion) is compared with the black liquor upgrading (via) gasification process for ammonia production in terms of economics, exergy efficiency and environmental impact. The combined energy integration and exergy analysis is used to identify the potential improvements that may remain hidden to the energy analysis alone, namely, the determination and mitigation of the process irreversibility. As a result, the exergy efficiencies of the conventional and the integrated cases average 40% and 42%, respectively, whereas the overall emission balance varies from 1.97 to −0.69 tCO2/tPulp, respectively. The negative CO2 emissions indicate the environmental benefits of the proposed integrated process compared to the conventional kraft pulp mill.

Keywords: entrained flow gasifier; black liquor; kraft pulp; exergy; ammonia; renewability; decarbonisation; energy integration; fertilisers; environmental impact.

DOI: 10.1504/IJEX.2021.115083

International Journal of Exergy, 2021 Vol.35 No.1, pp.35 - 65

Received: 23 Dec 2019
Accepted: 21 May 2020

Published online: 06 May 2021 *

Full-text access for editors Access for subscribers Purchase this article Comment on this article