Question

Q1. Compressors powered by natural gas engines are increasing in popularity. Several major manufacturing facilities have already replaced the electric motors that drive their compressors with gas-driven engines in order to reduce their energy bills since the cost of natural gas is much lower than the cost of electricity. Consider a facility that has a 130-kW compressor that runs 4400 h/yr at an average load factor of 0.6. Making reasonable assumptions and using unit costs for natural gas and electricity at your location, determine the potential cost savings per year by switching to gas-driven engines. (TOTAL 25 MARKS)

Answer 1

first we calculate the energy consumed by the compressor in kWh in a year

if the average load factor is 0.6 then

Therefore the total cost by electricity, assumption the cost of the electricity in $0.07/kWh and a cost of approximately one seventh of the cost of electricity for demand prices, then

1) cost of the energy consumed: 572000 kWh x $0.07/kWh = $40040/yr

2) cost of demand: 108.82kW x 4400h/yr x $0.01/kWh = $4788.08/yr

3) Total cost by electricity: $44828.08

If change for natural gas the energy equivalent in BTU of one kWh is 1kWh = 3412.14 BTU

1 BTU it cost $2.7/million BTU then

1) cost of the energy consumed

2) cost of demand:

3) the total cost by natural gas consumption is $9680.46 in one year

This price represents approximately 21% of the total cost of electricity, that is, there is a saving of 79% in energy costs when using natural gas engines.