Energy and Environment II               Answers in Red

QUIZ #5

 

1.      (2 points)

A.            FALSE: Total moles are conserved during combustion.

 

B.  TRUE: Total mass is conserved during combustion.

 

2.      (3 points)  The three major waste fuels burned for energy at mills operated by the forest and paper products industry are:

 

A. Bark

 

B. Sawdust & Sanderdust

 

C. Black Liquor

 

3.      (3 points) The three major types of thermochemical processes applied to biomass are:

 

A. Direct Combustion

 

B. Pyrolysis

 

C. Gasification

 

4.      (7 points) Consider the equation:      P = h r g Q H

State the energy system to which this equation applies:

Hydroelectric

Identify each term in the equation and gives its units so that the equation is correct:

P = Power output (of turbine or generator) as watts

 

h = Efficiency (of turbine or turbine with generator) as decimal (unit-less)

 

 

r = Density of water as kg/m3

 

 

g = Acceleration of gravity as m/s2

 

 

Q = Volumetric flow of water as m3/s

 

 

H = Head of water (with friction effect subtracted) as m.

 

5.      (5 points)  For seas off the southern coast of Australia, for which the average power per crest length is 75 kw/m, we found in HW#9 the wave height, H, to be about 3 m.  What if the wave height were only 2 m, what would be the wave power per crest length?  BE SURE TO SHOW YOUR ANALYSIS.

 

For waves, the power per crest length is proportional to the wave height squared.  Thus:

 

P/75 = (2/3)2 = 4/9.

 

Thus: P = 75 x 4/9 = 33 kw/m

 

 

6.      (5 points)  Consider biomass grown in a laboratory under nearly ideal conditions.  Estimate the overall efficiency of converting the solar energy (or simulated solar energy) to the chemical energy of the biomass grown in the lab.  There are four considerations involved.  List these and their individual efficiencies.  Then give the overall efficiency.

 

A. Reflection and transmission of sunlight at leaves, leaving about 75-85% of the solar energy absorbed by the leaves.

 

B. Only about 50% of the energy of the photons can be used by the photosynthetic process – some is too long, some of the short wavelength radiation is excessive.

 

C. The conversion of the photon energy active in photosynthesis to the chemical energy of the carbohydrate material grown is about 30% (ie 4.8/14.4-to-18).

 

D. In order for the plants to sustain themselves, they consume about 40 to 50% of their energy.

 

Overall efficiency: This gives an overall efficiency of about:

0.80 x 0.50 x 0.30 x 0.55 @ 0.07 (about 10% was stated in class based on data shown).