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Chemical Engineering 341 Design For Environment Question



Short Answer Section (Closed book)

l.) (10 points) In class and in your text, five tiers of costs that are relevant to the evaluation of the environmental benefits of projects were identified. Identify these five tiers of costs, describe the nature of the costs, give an example associated with each tier and describe the level of uncertainty associated with estimating the costs.a) Tie-R 1 —e D zze-er- C05TS

2. (5 points) Draw a typical cycle used in a heat pump. the inlet enthalpy, outlet enthalpy, and work input. Label appropriate temperatures and define the coefficient of performance.


Beiru Heated

IHeat Dewered Hge)

Expansion Vahte

(koat Acq)tgd Here)



Beng Cooled


I-Eat Deltærgd to Heat Pump = oondenger, praüi1J teat a

3. (5 points) (5 points) Draw a typical combined heat and power configuration, labeling the electricity generation and heat output. Compare the CHP configuration to a conventional electric power generating facility. Describe factors that limit the ability to implement combined heat and power applications.


4. (5 points) Lurmann, et al. (1999) have estimated the costs associated with ozone and fine particulate matter concentrations above the National Ambient Air Quality Standards (NAAQSs) in Houston. They estimated that the economic impacts of early mortality and morbidity associated with elevated fine particulate matter concentrations (above the NAAQS) are approximately $3 billion/year. Hall, et al. (1992), performed a similar assessment for Los Angeles. In the Houston study, Lurmann et al examined the exposures and health costs associated with a variety of emission scenarios. One set of calculations demonstrated that a decrease of approximately 300 tons/day of fine particulate matter emissions resulted in a 7 million person-day decrease in exposure to particulate matter concentrations above the proposed NAAQS for fine particulate matter, 17 less early deaths per year, and 24 fewer cases of chronic bronchitis per year. Using estimated costs of $300,000 per case of chronic bronchitis and $6,000,000 per early death, estimate the social cost per ton of fine particulate matter emitted.

Net Cost Reduction = (17 less early deaths/yr)( $6,000,000 per early death) + (24 chronic bronchitis cases per year)($300,000 per case of chronic bronchitis) = $109.2x106/yr.

Social Costs Per Ton Emitted: ($ tons/day)(365 days/yr)] $997.26/ton.

5. (5 points) A chemical manufacturing facility buys raw material for $0.60 per pound and produces 90 million pounds per year of product, which is sold for $0.75 per pound. The process is typically run at 90% selectivity and the raw material that is not converted into product is disposed of at a cost of $0.80 per pound (by incineration). A process improvement allows the process to be run at 98% selectivity, allowing the facility to produce 98 million pounds per year of product. What is the net revenue of the facility (product sales - raw material costs - waste disposal costs) before and after the change? How much of the increased net revenue is due to increased sales of product and how much is due to decreased waste disposal costs?

Original Process: 90% selectivity.

Net Revenue (per 1b product) = selling price - raw matls. cost - waste treatment costs ($0.75/lb prod.) - prod. prod.

($0.75/lb product - $0.667/lb product - $0.089/lb product $-0.006/lb product

Improved Process: 98% Selectivity.

Net Revenue (per 1b product) = selling price - raw matls. cost - waste treatment costs ($0.75/lb prod.) - feed) waste)

= ($0.75/lb product - $0.612/lb product - $0.016/1b product $0.122/1b product

6. (10 points) Water use and treatment in a polyester yarn dyehouse, described by Wenzel, et al, (2002), will be used as a case study of water reuse design methods. The first task in the analysis is to define the current uses (sinks) of water in the process. For each stream, the flow rate, and the inlet and outlet concentrations of suspended solids (a key contaminant) are required. Data for the yarn facility are shmvn in Table 1.

Table 1. Water use and total solids (TS) contamination levels (entering and exiting each

rocess ina 01 ester arnd ehouse is described in the data below.


Flow m3/ ear

TS m I

D ebath

1 oo,ooo


Reductive rinse


Hot rinse



Cold rinse


Yarn lubrication



  • From these data, begin the construction of a "pinch" diagram by calculating the amount of contaminant loading in the sink streams at each concentration level of contamination. For example, in the concentration range between 400 and 600 mg/l, there is one stream adding contaminant mass to water (Cold rinse). The total mass of contaminant transferred into this stream in this concentration range is product of the flow rate 200,000 m /yr and the concentration change (600-400 mg/L). A total of 40,000 kg/yr (200,000 m3/yr * (.6-.4) kg/m3) is transferred. Calculate the amounts of mass transferred in each of the concentration ranges defined by Table 2.
  • Construct a composite rich stream diagram, by representing the mass transferred in each region as a vector in a plot of concentration (vertical axis) and mass transferred (horizontal axis). For example, the vector representing the concentration range of 400-600 mg/l, described in part a.), would begin at a concentration of 400 mg/l and zero mass exchanged, and would extend to a concentration of 600 mg/l and 40,000 kg/yr of mass exchanged. Draw the vectors for each region head to tail to give a composite sink vector. This vector should begin at a concentration of 250 mg/l and mass transferred of zero and extend to a concentration of 5000 mg/l and total mass transferred of 350,000 kg/yr.

a.) There are 4 concentration regions:

Region 1:

400-600 mg/L

One stream in this region (Cold rinse)

Total flow rate of 200,000 m3/yr

Total mass exchanged of 40,000 kg/yr

Region 2:

600-1000 mg/L

Two streams in this region (Hot rinse and Yarn lube)

Total flow rate of 200,000 m3/yr

Total mass exchanged of 80,000 kg/yr

Region 3:

1000-2000 mg/L

Two streams in this region (Dyebath and Hot rinse)

Total flow rate of 200,000 m3/yr

Total mass exchanged of 200,000 kg/yr

Region 4:

2000-5000 mg/L

One stream in this region (Reductive rinse)

Total flow rate of 10,000 m3/yr

Total mass exchanged of 30,000 kg/yr










100000 150000 200000 250000

Mass exchanged (kg/yr)

300000 350000 400000



(Open book)

  1. (25 points) Design a mass exchange network for the following rich and lean streams:

Yin (rich) or Xin (lean) Yin (rich) or Xin (lean) flow rate

(mass fraction) (mass fraction) (kg/s)

.04 .0 3

.09 .04 3

.05 6

  • Draw a composition interval diagram
  • Determine the pinch point, assuming that the following equilibrium relationships hold:
  • Determine the process mass exchanged if the minimum driving force is 0.
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