Transformation of biosolids to biochar: A case study

Abstract

This case study examines the feasibility of the production of biochar from biosolids using energy neutral pyrolysis process using ASPEN Plus process modeling followed by a detailed techno‐economic assessment. The modeling exercise demonstrated that the pyrolysis can be energy neutral with moisture content in biosolids as high as 50 wt.%. In the case of moisture content lower than 50%, surplus energy will be available which can be converted to electrical energy; generating additional revenue. Further analysis on the effect of pyrolysis temperature on surplus energy available revealed that surplus energy increased when pyrolysis temperature reached from 450 to 650°C, but it gradually decreased above 650°C. The techno‐economics analysis suggested that biosolids management cost and biochar sale price were the most critical sensitivity factors while capital and operating costs of the pyrolysis unit seemed to be less critical. The positive Net Present Value values in scenario modeling suggest that the conversion of biosolids to biochar using energy neutral pyrolysis process looks promising and is techno‐economically feasible for most of the studied scenarios. © 2018 American Institute of Chemical Engineers Environ Prog, 38:e13113, 2019

Functional Biochar and Its Balanced Design

“…This huge variation results from the expenses of the feedstocks and production conditions (mostly determined by the techniques related to the oven, such as control accuracy of the atmosphere and temperature). The increase of pyrolysis temperature could increase the biochar production cost . The cost of biochars derived from crop residues and woody waste increased from $1.00/kg to $1.30/kg with the pyrolysis temperature increasing from 400 to 700 °C.…”

“…The increase of pyrolysis temperature could increase the biochar production cost. 97 The cost of biochars derived from crop residues and woody waste increased from $1.00/kg to $1.30/kg with the pyrolysis temperature increasing from 400 to 700 °C. The cost of sludge derived biochar increased from $0.70/kg to $ 1.00/kg with the same pyrolysis temperature increment ( Table 3 ).…”

Pyrolysis Solves the Issue of Organic Contaminants in Sewage Sludge while Retaining Carbon—Making the Case for Sewage Sludge Treatment via Pyrolysis

“…The moisture content of sewage sludge and biosolids (treated sewage sludge) can be >95%, and drying prior to thermal treatment is necessary. Drying is a very energy intensive stepit can consume 5-times more energy than is needed for the pyrolysis processtherefore the treatment of wet sewage sludge via pyrolysis requires external energy addition. − There are many different technologies for drying sludge with vastly different energy requirements. ,, Solar drying techniques need little energy input yet have disadvantages, such as long processing times and dependence on weather conditions. ,− Holistic process optimization, for example through utilizing excess heat from the pyrolysis unit to partially dry the feedstock improves economic and environmental considerations of sewage sludge pyrolysis. ,, …”

“…Consequently, when pyrolysis liquids and gases are combusted to power the reactor, the pyrolysis process itself produces energy . A modeling study suggests that sewage sludge pyrolysis can be energy positive if the starting moisture content is <50% . Therefore, in particular at wastewater treatment plants where dried sewage sludge pellets/granules are already produced, e.g., as means to reduce the product volume, pyrolysis of the material is a natural next step.…”

Untitled

“…To overcome this problem, biomass needs to be processed further by improving the quality of production of energy conversion materials. Thermochemical conversion of energy from biomass consists of pyrolysis technology [6]- [9], gasification [10]- [12], torefaction [13]- [16], Hydrothermal carbonization [17]- [20], and direct combustion [21]- [24].…”