Question

PLEASE READ THIS CAREFULLY FIRST BEFORE ANSWERING!!!!!! A DOWN VOTE WILL BE GIVEN IF YOU JUST PASTE AN ANSWER WITHOUT JUSTIFYING IT LIKE I'M ASKING FOR.

I know this question is already on here but i have seen too many differing answers for a) and ultimately b) & c) so i am after justification for your answer that you provide. The main answers i have seen for a) are 35955.4 Kg/Hr and 44398.3 Kg/Hr dependant on which side they put the 0.9. Again please justify why you put the 0.9 on the side you do.

For b) i have seen 2 differing answers also of 1134.8 and 619 depending on if they convert to Kelvin or not. Again please explain why if you do or don't do so.

a) Dry sat steam at 180 degrees is to be produced in a fire tube boiler from the cooling of 50000 kg h-1 of flue gases from a pressurised combustion process. the gases enters the tubes of the boiler at 1600 degrees and leave at 200 degrees. The feed water is externally pre-heated to 180 degrees before entering the boiler.

The specific heat capacity of the flue gases is 1.15 kj kg^-1 k^-1

The latent heat of vapourisation of the water at 180 degrees is 2015 kj kg^-1

Feed water temp 180 degrees.

Determine amount of steam produced per hour, if total heat loss is 10 percent of the heat available for steam raising.

b) The overall heat transfer coefficient based on the outside area of the tubes is given as 54 Wm^-2K^-1. Determine the area of heat transfer required to perform this duty

c) The tubes within the boiler are to be 25 mm inside diameter with a wall thickness of 3 mm. The average flue gas velocity through the tubes to maintain the overall heat transfer coefficient value and to minimise pressure losses is to be more than 22 m s–1 and less than 28 m s–1 .

Assuming that the average density of the flue gases is 1.108 kg m–3 , calculate:

i) the minimum and maximum number of tubes in each pass

ii) the overall length of tubes at each of these numbers of tubes

iii) the minimum number of tube passes in each case, if the length of a boiler tube is to be less than 5 metres.

Answer 1