Energy Return on Investment and Techno-economics of Pellet Production from Steam Pretreated Biomass

Research SummaryCo-firing biomass pellets with coal has been considered a method to reduce GHG emissions. However, pellets have low calorific value and bulk density and so are not suitable for co-firing. In this research, steam pretreatment was considered as a suitable process to evaluate the economic impact of the pretreatment process on the overall supply chain.

The main objectives of the research were to develop a process model to evaluate specific energy consumption of steam pretreatment and compare it with regular pellet production at various scales. The specific objectives were to develop a process model for stream pretreatment of ligno-cellulosic biomass for pellet production, evaluate energy and mass balance of the steam pretreated pellet production process, calculate the NER of the streampretreated pellet production process, develop a data-intensive techno-economic model to evaluate production costs, estimate pellet production cost ($ tonne-1 and $ GJ-1) for three feedstocks, determine the optimum pellet production size from three feedstocks through two processes: steam pretreated and regular pellet production.

The techno-economic model indicates that the process production cost (calculated in $ GJ-1) is on par with the production cost for both regular and steam pretreated production processes. The major cost contributor for steam pretreated production costs are capital, energy, and delivered costs. Optimizing drying and steam pretreatment energy costs can significantly improve the production cost.

Major ResultsThe steam pretreatment process was found to be energy intensive. The net energy ratio (NER) was calculated for both processes. The NER of the steam pretreated pellet process was found to be 1.29, while the NER of the regular pellet process was found to be 5.0. The major reason for this deviation is the high energy requirement of the steam pretreatment and drying units.

ConclusionThe results obtained here through process modeling and techno-economic studies would help optimize the design and operation of a commercial pellet plant with the addition of the steam pretreatment process.

Name Degree Year Supervisor

S M Hassan Shahrukh M.Sc. 2015 Dr. Amit Kumar

Department ofMechanical Engineering

Schematic flowchart of the developed steam pretreatment model. The boiler is represented as a heater unit and the steam pretreatment unit considered is a yield reactor.

Process net energy ratio (NER) falls as temperature increases. The major contributor of the energy input is from the steam pretreatment and drying units.

Comparison of $ GJ-1 cost between steam pretreated and regular pellets.

AcknowledgementThe authors are grateful to BiofuelNet Canada and the University of Alberta for the financial support.

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Biomass Collection, Processing andTransportation