Elementary Principles of Chemical Processes, Binder Ready Version
Elementary Principles of Chemical Processes, Binder Ready Version
4th Edition
ISBN: 9781118431221
Author: Richard M. Felder, Ronald W. Rousseau, Lisa G. Bullard
Publisher: WILEY


Textbook Question
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Chapter 9, Problem 9.83P

The wastewater treatment plant at the Ossabaw Paper Company paper mill generates about 24 tonnes of sludge per day. The consistency of the sludge is 35%, meaning that the sludge contains 35 wt% solids and the balance liquids. The mill currently spends $40/tonne to dispose of the sludge in a landfill. The plant environmental engineer has determined that if the sludge consistency could be increased to 75%, the sludge could be incinerated (burned) to generate useful energy and to eliminate the environmental problems associated with landfill disposal.

A flowchart for a preliminary design of the proposed sludge-treatment process follows. For simplicity, we will assume that the liquid in the sludge is just water.

Chapter 9, Problem 9.83P, The wastewater treatment plant at the Ossabaw Paper Company paper mill generates about 24 tonnes of Process description: The sludge from the wastewater treatment plant (Stream (A) passes through a dryer where a portion of the water in the sludge is vaporized. The heat required for the vaporization comes from condensing saturated steam at 4.00 bar (Stream (B)). The steam fed to the dryer is produced in the plant’s oil-fired boiler from feedwater at 20°C (Stream (C)). The heat required to produce the steam is transferred from the boiler furnace, where fuel oil (Stream (D)) is burned with 25% excess air (Stream (E)). The concentrated sludge coming from the dryer (Stream (F)), which has a consistency of 75%, is fed to an incinerator. The heating value of the sludge is insufficient to keep the incinerator temperature high enough for complete combustion, so natural gas (Stream (G)) is used as a supplementary fuel. A stream of outside air at 25°C (Stream (H)) is heated to 110°C and fed to the incinerator along with the concentrated sludge and natural gas. The waste gas from the incinerator is discharged to the atmosphere.

Fuel oil: The oil is a low-sulfur No. 6 fuel oil. Its ultimate (elemental) analysis on a weight basis is 87% C, 10% H, 0.84% S, and the balance oxygen, nitrogen, and nonvolatile ash. The higher heating value of the oil is 3.75 × 104kJ/kg and the heat capacity is Cp= 1.8 kJ/(kg·°C).

Boiler: The boiler has an efficiency of 62%, meaning that 62% of the heating value of the fuel oil burned is used to produce saturated steam at 4.00 bar from boiler feedwater at 20°C. Fuel oil at 65°C and dry air at 125°C are fed to the boiler furnace. The air feed rate is 25% in excess of the amount theoretically required for complete consumption of the fuel.

Sludge: The sludge from the wastewater treatment plant contains 35% w/w solids (S) and the balance liquids (which for the purposes of this problem may be treated as only water) and enters the dryer at 22°C. The sludge includes a number of volatile organic species, some of which may be toxic, and has a terrible odor. The heat capacity of the solids is approximately constant at 2.5 kJ/(kg·°C).

Dryer: The dryer has an efficiency of 55%, meaning that the heat transferred to the sludge, 02, is 55% of the total heat lost by the condensing steam, and the remainder, Q ˙ 3 , is lost to the surroundings. The dryer operates at 1 atm, and the water vapor and concentrated sludge emerge at the corresponding saturation temperature. The steam condensate leaves the dryer as a liquid saturated at 4.00 bar.

Incinerator: The concentrated sludge has a heating value of 19,000 kJ/kg dry solids. For a feed sludge of 75% consistency, the incinerator requires 195 SCM natural gas/tonne wet sludge [ 1 SCM = 1 m3(STP)]. The theoretical air requirement for the sludge is 2.5 SCM air/10.000 kJ of heating value. Air is fed in 100% excess of the amount theoretically required to bum the sludge and the natural gas.

Use material and energy balances to calculate the mass flow rates (tonnes/day) of Streams (B), (C), (D), (E), (F), (G) and (H), and heat flows Q ˙ 0 , Q ˙ 1 , ..... , Q ˙ 4 ( k J / d a y ) . Take the molecular weight of air to be 29.0. (Caution: Before you start doing lengthy and unnecessary energy balance calculations on the boiler furnace, remember the given furnace efficiency.)Exploratory Exercises—Research and Discover

  1. The money saved by implementing this process will be the current cost of disposing of the wastewater plant sludge in a landfill. Two major costs of implementing the process are the installed costs of the new dryer and incinerator. What other costs must be taken into account when determining the economic feasibility of the process? Why might management decide to go ahead with the project even if it proves to be unprofitable?
  2. What opportunities exist for improving the energy economy of the process? (Hint: Think about the need to preheat the fuel oil and the boiler and incinerator air streams and consider heat exchange possibilities.)
  3. The driving force for the introduction of this process is to eliminate the environmental cost of sludge disposal. What is that cost—that is, what environmental penalties and risks are associated with using landfills for hazardous waste disposal? What environmental problems might incineration introduce?

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Chapter 9 Solutions

Elementary Principles of Chemical Processes, Binder Ready Version

Ch. 9 - Prob. 9.11PCh. 9 - Prob. 9.12PCh. 9 - In the production of many microelectronic devices,...Ch. 9 - Prob. 9.14PCh. 9 - Prob. 9.15PCh. 9 - Prob. 9.16PCh. 9 - Prob. 9.17PCh. 9 - Carbon monoxide at 25°C and steam at 150°C are fed...Ch. 9 - Prob. 9.19PCh. 9 - Prob. 9.20PCh. 9 - Ethyl alcohol (ethanol) can be produced by the...Ch. 9 - Prob. 9.22PCh. 9 - Prob. 9.23PCh. 9 - Prob. 9.24PCh. 9 - Formaldehyde is produced commercially by the...Ch. 9 - Prob. 9.26PCh. 9 - Prob. 9.27PCh. 9 - Prob. 9.28PCh. 9 - Prob. 9.29PCh. 9 - A gas mixture containing 85 mole% methane and the...Ch. 9 - Ethylene oxide is produced by the catalytic...Ch. 9 - Cumene (C6H5C3H7) is produced by reacting benzene...Ch. 9 - Ethylbenzene is converted to styrene in the...Ch. 9 - Prob. 9.34PCh. 9 - Prob. 9.35PCh. 9 - Prob. 9.36PCh. 9 - Prob. 9.37PCh. 9 - Coke can be converted into CO—a fuel gas—in the...Ch. 9 - Prob. 9.39PCh. 9 - Prob. 9.40PCh. 9 - Prob. 9.41PCh. 9 - The equilibrium constant for the ethane...Ch. 9 - You are checking the performance of a reactor in...Ch. 9 - Hydrogen is produced in the steam reforming of...Ch. 9 - Prob. 9.45PCh. 9 - Five cubic meters of a 1.00-molar aqueous sulfuric...Ch. 9 - Prob. 9.47PCh. 9 - Prob. 9.48PCh. 9 - Prob. 9.49PCh. 9 - Calcium chloride is a salt used in a number of...Ch. 9 - A dilute aqueous solution of sulfuric acid at 25°C...Ch. 9 - A 2.00 mole% sulfuric acid solution is neutralized...Ch. 9 - A 12.0-molar solution of sodium hydroxide (SG =...Ch. 9 - Citric acid (C6H8O7) is used in the preparation of...Ch. 9 - Ammonia scrubbing is one of many processes for...Ch. 9 - Various uses for nitric acid are given in Problem...Ch. 9 - A natural gas is analyzed and found to consist of...Ch. 9 - Prob. 9.58PCh. 9 - A fuel gas is known to contain methane, ethane,...Ch. 9 - A fuel gas containing 85.0 mole% methane and the...Ch. 9 - A mixture of air and a fine spray of gasoline at...Ch. 9 - The heating value of a fuel oil is to be measured...Ch. 9 - Methanol vapor is burned with excess air in a...Ch. 9 - Methane at 25°C is burned in a boiler furnace with...Ch. 9 - Methane is burned completely with 40% excess air....Ch. 9 - A gaseous fuel containing methane and ethane is...Ch. 9 - A coal contains 73.0 wt% C, 4.7% H (not including...Ch. 9 - A mixture of methane, ethane, and argon at 25°C is...Ch. 9 - Prob. 9.69PCh. 9 - Prob. 9.70PCh. 9 - Prob. 9.71PCh. 9 - A bituminous coal is burned with air in a boiler...Ch. 9 - Prob. 9.73PCh. 9 - A natural gas containing 82.0 mole% CH4and the...Ch. 9 - Prob. 9.75PCh. 9 - Liquid n-pentane at 25°C is burned with 30% excess...Ch. 9 - Methane is burned with 25% excess air in a...Ch. 9 - Methane and 30% excess air are to be fed to a...Ch. 9 - Prob. 9.79PCh. 9 - In Problem 9.79, the synthesis of methanol from...Ch. 9 - Natural gas that contains methane, ethane, and...Ch. 9 - Prob. 9.82PCh. 9 - The wastewater treatment plant at the Ossabaw...

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