Honors Theses and Capstones

Date of Award

Spring 2013

Project Type

Senior Honors Thesis

College or School

CEPS

Department

Chemical Engineering

Program or Major

Bioengineering

Degree Name

Bachelor of Science

First Advisor

Professor P.T. Vasudevan

Abstract

It is well known that the United States’ dependence on crude-oil negatively affects its economy, safety, and environment. To alleviate these negative consequences, a more economical and environmentally-friendly source of fuel, such as biomass, should be explored. The conversion of biomass to bio-oils involves the pyrolysis of biomass at about 500°C, thus requiring a great deal of heat. This heat source could be the excess waste heat from a coal gasifier.

As such, this report specifies the design of an industrial plant that produces bio-oils from biomass by using the waste heat from a coal gasifier. It is designed to produce 2.24×108 kg/yr of bio-oil that can be sold at $0.79/kg. This plant involves coal and biomass solids handling, a coal gasification reactor, a biomass pyrolysis reactor, and a series of separation units to remove waste products from the syngas and isolate the bio-oil. The syngas contains methane, hydrogen, and carbon monoxide and is sold as a by-product credit. The plant is expected to run on feeds of 1.5x1011 kg/yr of coal and 5.4 x108 kg/yr of raw biomass.

The coal gasification reactor was sized based on the heating duty of steam at 273000 kJ/s and the biomass pyrolysis reactor was sized based on a heating duty of 7026 kJ/s. The plant’s operating factor (POF) is 0.9 at 7884 hrs/yr running 24 hrs/day and 328.5 days/yr. The total bare module equipment cost, including all pumps, heat exchangers, grinders, separators, absorber, and reactors is $93 million. The total capital investment of the plant is $173 million. The DCFRR and NRR are 12.59% and 20% respectively.

Given that selling price of bio-oil ($0.79/kg) associated with this plant is about six times more expensive that the average cost of bio-oil ($0.13/kg), it is not recommended that a Class – 1 Estimate be conducted. Before a Class – 1 Estimate can be conducted, the unnecessary costs associated with this proposed plant must be addressed and reduced. Specific attention must be paid to the following two heat exchangers, E-127 and E-129. Additionally, attention should be given to discover a cheaper source of industrial, liquid oxygen.

Comments

The safety considerations include:

  • Insulation on gasification product lines due to high temperatures.
  • Spring loaded relief values and bursting discs on all vessels to prevent built up pressure and on storage vessels to prevent backflow.
  • Pressure relief valves on the discharge side of pumps, compressors, and turbines .
  • Double block and bleeds on feed lines and cool lines exposed to heat.
  • Control system, with PID controls, on gasification and pyrolysis reactor to monitor and control their pressure and temperature by adjusting the cooling water to reactor jackets and the feed flow rates.
  • Additional temperature and pressure gauges on the reactor for manual monitoring by the operator.

The key, innovative design features include:

  • Waste heat, in the form of steam, from the gasifier used to heat the biomass.
  • Bio-char from the pyrolysis of biomass recycled to the gasifier to decrease the amount of raw coal fed and, consequently, the cost of raw materials.
  • Bio-gas from the pyrolysis of biomass used to dry the raw biomass to a moisture content of 10% as well as to blow the biomass up through the fluidized bed.

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