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18 Nov 2019

Gas boiler uses methane (CH4) as its fuel source. As a newly appointed engineer, you are assigned by your superior to determine whether the current boiler operation is running at the optimum conditions. You are given the average daily Orsat gas analysis of the stack gas as shown in Table Q3.

Table Q3: Composition of Orsat stack gas.

Component Mol (%)

CH4 0.55

O2 12.00

N2 82.40

CO2 5.05

Given the element molecular weight of C=12, H=1, O=16 and N=14. Assume the air stream fed to the boiler only consists of 21 mol% O2 and 79 mol% N2. In order to perform the analysis, you need to solve few fundamental question below.

a. Write the main stoichiometric combustion reaction.

b. Draw the input-and output flowchart of the process.

c. By using element balances and taking 100 kmol/s of Orsat flue gas as the basis of calculation, determine the following:

i. The mass flow rate of natural gas into the boiler.

ii. The percentage of excess air used in the combustion

iii. The actual fractional conversion of methane

iv. The actual water produced.

v. Composition of stack gas in wet basis.

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Beverley Smith
Beverley SmithLv2
13 Jun 2019

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Related questions

Question 1
100 mol of pure methane (CH4) is burned in a furnace with 1000 mol of dry air. Some of the energy liberated by the combustion reaction is used to heat a process stream which flows through the furnace in tubes as shown below. An analysis of the waste gases shows that no methane is present in the waste stream.

a) State and balance the reaction equation for the complete combustion of methane at 25°C and include state symbols.

b) Determine the stoichiometric oxygen demand.
c) Calculate the percentage excess of oxygen.
d) Given the heat of formation data shown in table 1 (overleaf) calculate the heat of

combustion of methane.
e) Calculate the composition of the waste gases leaving the boiler.

The fuel is now changed to Butane gas which is fed to the furnace at a rate of 1 mol min-1 with 20% excess air. The combustion reaction goes to completion. The butane and air both enter the furnace at 25°C. The (wet) waste gas composition is given in table 1 below and the volumetric flowrate of the waste stream is found to be 0.896 m3min-1 at 0°C and 1 atm.

f) If the furnace is well insulated and the temperature of the waste gas stream is measured to be 600°C, how much energy is being transferred to the process stream each minute.

Table 1: Waste gas composition for butane feed.

Component

mol %

N2

74

O2

3

CO2

10

H2O

13

DearChegg Lifesaver. Here are the requirements:

1.Use given values as stated in questions below.

2.Clearly State Answer

3.(Please) LEAVE A COMMENT if you are currently working on anyproblems.

4.Formany of these problems you will need to use tabulated thermodynamicdata. Use the Information provided after problem 17.



---------------------------------------Questions---------------------------------------------------



1.Write a balanced formation equation for HNO3 at standardconditions. For the answer, enter the sum all of the coefficientsin the balanced equation. (If thisis not an integer, enter it as a decimal, not a fraction.)


2.Calculate ?H° for the following reaction:

SiO2(s)+ 4HF(g) ? SiF4(g) + 2H2O(g)


3.Use heat of formation data to determine ?H° for the reaction:

2NH3(g)? N2(g) + 3H2(g)


4.Calculate the mass of methane that must be burned to provide enoughheat to convert 330.0 g of water at 37.0°C into steam at 124.0°C.(Assume that the H2Oproduced in the combustion reaction is steam rather than liquidwater.)


5.Acetylene burns in air according to the following equation:

C2H2(g)+ 5/2 O2(g) ? 2 CO2(g) + H2O(g)

with?H° = -1255.8 kJ.

Giventhat ?Hf° for CO2(g) = -393.5 kJ/mol and ?Hf° for H2O(g) is -241.8kJ/mol, what is ?Hf° for C2H2(g)?






6.Given the following data:

HNO3(l)? 1/2N2(g) + 3/2O2(g) + 1/2H2(g) ?H° = 174.1 kJ

2N2O5(g)? 2N2(g) + 5O2(g) ?H° = -28.4 kJ

H2O(l)? H2(g) + 1/2O2(g) ?H° = 285.8 kJ


Calculate?H° for the reaction:

2HNO3(l)? N2O5(g) + H2O(l)

Notethat you should be able to answer this one without needing to useany additional information from the thermo table.


7.Hydrocarbons containing halogens are very useful molecules insynthetic chemistry. Use tabulated thermodynamic data as needed tocalculate ?Hf° for the reactionproduct in the equation shown below if ?H° for the reaction is-177.66 kJ.

C2H4(g)+ Cl2(g) ? CH2ClCH2Cl(g)



8.Identify the following statements as true or false. (Use thedrop-down menu and select "True" or "False" for each. You must getall 6 correct.)

Allsystems become more disordered spontaneously.

Both?Ssys and ?Ssurr must equal zero at equilibrium.

Theentropy of the universe is constant; the energy of the universedecreases towards a minimum.

Allspontaneous processes release heat.

Ifa reaction is spontaneous, the reverse reaction is non-spontaneous.

Ifa process decreases the randomness of the particles of a system,the entropy of the system increases.


9.Use tabulated thermodynamic data to calculate ?S° for the reaction:

PbO2(s)+ 2Ni(s) ? Pb(s) + 2NiO(s)



10.Calculate ?S° for the combustion of ethane (C2H6) to form carbondioxide and gaseous water.



11.Urea ((NH2)2CO) can be formed from ammonia and carbon dioxide asshown in the following reaction. The ?H° value for this synthesisis -134.0 kJ. Calculatethe ?H°f for urea.

2NH3(g)+ CO2(g) ? (NH2)2CO(s) + H2O(l)


12.The ?S° value for urea the synthesis reaction above is -424.0 J/K.Calculate S° for urea.

Tries0/99


13.Calculate ?G° for the synthesis of urea under standard conditions(298 K and 1 atm).

Tries0/99


14.Compute the standard free energy change for the following reaction.

O3(g)+ NO(g) ? NO2(g) + O2(g)

Tries0/99


15.The most important commercial process for generating hydrogen gasis the water-gas shift reaction:

CH4(g)+ H2O(g) ? CO(g) + 3H2(g)

Usetabulated thermodynamic data to find ?G° for this reaction at thestandard temperature of 25°C.


16.Now calculate ?G°1100 for this process when it occurs at 1100 K.


17.The molar enthalpy of fusion (?H°) of fluorine is 0.260 kJ/mol, andthe molar entropy of fusion (?S°) of fluorine is 4.851 J/mol K.Using this information,estimate the freezing point of fluorine. (You must answer inKelvin.)

1. A sludge containing 4% solid (by weight) needs to be thickened by centrifugation to ≥15% solid for disposal. The centrifuge has a high constant speed and produces a dewatered sludge containing 20% solid. To increase the processing capacity while still meeting the disposal requirement, you decide to bypass (i.e., not dewater) some of the feed sludge and blend the untreated sludge with the dewatered (20% solid) sludge, so as to produce a final sludge with a 15% solid content. Assume all sludge streams have the density of water.

(a) Give the centrate production rate (in L/min) and the percent solid (of the total coming in) discharged via the centrate?

(b) What % of the feed sludge is bypassed (i.e., not centrifuged)?

2. Eutrophication is a natural aging process all lakes undergo as nutrients and organic matter accumulate from their drainage basins. Over time the accumulated nutrients enable increased aquatic growth and stimulate biological activities. The increase in phytoplankton causes the lake to become murky, while decaying organic matter depletes the available dissolved O2. Further accumulation of silt, nutrients, and organic matter causes the eutrophic ("well-fed") lake to become shallower and warmer with more plants growing in the shallow edges. This process transforms lakes into bogs and marshes over time. Natural eutrophication is usually quite slow, often measured in thousands of years before major changes occur. What human activity has done is rapidly accelerate this process (called "cultural eutrophication") by introducing large quantities of nutrients. Sources of nutrients include municipal wastewater, industrial wastes, and runoff from fertilized agricultural land. The introduction of superfluous nutrients disturbs the natural balance of the system, causing excessive algae growth and water quality deterioration. Algal blooms are the unsightly and often malodorous clumps of rotting debris along the shoreline and thick mats of dead organic matter in the lake. A nutrient of major importance that enter fresh water bodies such as lakes from the aforementioned sources is phosphorous. C = 20% C = 15% Q = 100 L/min C = 4% bypass centrifuge C = 0.1% ("centrate") 2 Consider a phosphorus-limited lake with a surface area equal to 8 x 107 m 2 that is being fed by a stream with a flow rate of 15 m3 /s and a phosphorus concentration of 0.01 mg/L. An outfall from a wastewater treatment plant also adds 1 g/s of phosphorus to the lake, but its volumetric flow rate is small and can be ignored. The outflow rate from the lake is the same as the inflow (15 m3 /s). Because phosphorus can attach to suspended particles in lake water, the phosphorus in the lake can also be removed through particle settling (to sediment), which occurs at a rate of 10 m/yr. For the questions below, assume the lake is a cylindrical CSTR.

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