chemical enginneering

Project description
it is a project about chemical engineering. Project Description, CHE 410 Fall 2014

Mixtures of methane and carbon dioxide occur in a number of different fields. With growing concern regarding global warming, there is a drive to make use of these mixtures rather than venting them to the atmosphere. Expected limitations in future fossil fuel supplies, including natural gas (methane) further make it imperative that energy efficient, cost effective means be developed to utilize these mixtures. Your project will examine various ways to separate these mixtures to produce valuable streams of the pure (or relatively pure) components.

Examples of methane/carbon dioxide mixture sources:
– Most natural gas wells are contaminated with low to moderate levels of carbon dioxide, and therefore extracting these resources may provide a natural gas stream with excess carbon dioxide. – Enhanced oil recovery systems can extend the effective life of existing oil fields by pumping CO2 into the ground around the periphery of the field to force gas up through the existing well. The gas that leaves these wells contains methane but with very high levels of CO2. Depending on the status of the field, the concentrations of carbon dioxide and methane can vary substantially.
– Landfills can generate significant amounts of methane through anaerobic decomposition of the solid waste. This methane gas has similar levels of CO2 and methane, and is available at close to atmospheric pressure. This gas is often vented to the atmosphere, but with current concerns over global warming there is considerable interest in the possibility of upgrading this landfill gas for subsequent re-sale.

Our product development group has been exploring the possibility of purifying a number of gas streams containing mixture of CO2 and methane. Marketing has done some preliminary research on the potential markets for the purified CO2 and methane products that might be obtainable from this feed gas. There are several potential markets for methane depending on the product purity, with the estimated prices (based on the fuel value in MMBtu = 106 Btu) summarized in the Table below:

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Product CH4 concentrationPrice Specifications
Waste Gas< 10%—-
Low Energy Gas10 – 40%$2.6/MMBtu–
Medium Energy Gas40 – 70%$3.2/MMBtu–
High Energy Gas70 – 95%$3.8/MMBtu–
Pipeline Quality Gas95%$4.4/MMBtu600 psi
Liquified Natural Gas<50 ppm CO2$5.1/MMBtu600 psi

The market for CO2 is much more limited. High purity CO2 (99%) can be sold for use in the production of dry ice and other chemical applications. Price estimates are in the range of $0.004/SCF (SCF = standard cubic feet).

A variety of processes are available for the separation of the methane – CO2 feed gas. These include:

1 — cryogenic distillation
2 — absorption using water as the absorbent
3 — absorption using methyldiethanolamine solutions
4 — gas separation membranes
The potential economic advantages/disadvantages of these different processes remain to be determined. Your design team is to prepare a report on the preliminary economic evaluation of the available processes for the CO2 – methane separation (the specific properties of the feedstock to use in your group will be provided in the near future). Team assignments are included on the last page of this description.

Cost Information

Our Senior Design Engineers have compiled the following information on the capital and operating costs for the different separation processes.

Absorption:
This process will absorb CO2 into the MDEA solution, followed by regeneration of the MDEA such that the same solution can be reused. Capital costs for the adsorption columns are proportional to the costs of the packing material (1″ Rashig rings). These have been estimated as $1700/ft3 of column volume, and these rings will last 30 years. The cost of MDEA has been estimated at $1.00/kg MDEA, with the required MDEA inventory being 1 days worth (i.e. Inventory = LMDEA*1 day). The expected life of the MDEA solution (taking into account MDEA degradation and other losses) is one year. The only other significant operating costs are any heating (or cooling) and pressurization required to achieve the desired operating temperature and pressure. There is no cost associated with the MDEA regeneration, other than the fact that after 1 year the MDEA must be replaced due to degradation. For absorption with water, the cost of the column based on packing rings is equivalent. The cost of water should use the Cooling/Process Water below.

Cryogenic Distillation:
Capital Costs for the column have been estimated as $400,000/plate/year (each plate has to be replaced each year). Operating Costs in this system are dominated by the costs of refrigeration (i.e. the cost of the electricity required to supply the necessary refrigeration for the condenser). Documentation on estimation of cooling costs will be provided. If a flash unit is considered, the capital cost should be estimated as that of a single tray.

Gas Separation Membranes:
Membrane Costs are $3/ft2, with the expected life-time of the membranes being one year. The permeances (permeability divided by thickness) of the available polysulfone membranes are:

kCO2 = 2.5 x 10-11 mol/(cm2.sec.mm Hg)
kCH4 = 3.0 x 10-13 mol/(cm2.sec.mm Hg)

Operating Costs in this system are dominated by any required pressurization of the feed and/or permeate streams.

General Cost Data: Utility Cost_____
Electric$0.08/kilowatt-hr
Heating$3.0/MMBtu
Cooling/Process Water$0.15/1000 gal
Steam$3.5/1000 lb

Compression costs should be evaluated directly from the compressor power requirements. For a liquid stream this is simply:

Power = VL(P2 P1)

where VL is the liquid volumetric flowrate. The energy requirements for a gas compressor are:

Energy per mole compressed = RT ln(P2/P1)

where P2 is the pressure after the compressor and P1 is the pressure of the stream entering the compressor. Cooling and heating requirements should be determined based on the heat of vaporization (or condensation) along with the energy required to change the temperature (CpT). Please provide references for all thermodynamic and physical property information.

Grading

Most project teams have 4 students, with each student given primary responsibility for one of the four separation options. Teams with 3 members only need to consider 3 options, and can choose which 3. Your grade on the Project will consist of two separate components: