Calculate BTU

Homework alert!

Are we to include the BTU required to heat the 160 water up again?

Aaaaand, the inevitable question… why not simply use that heat source to bring your process water up to 150F?

This is waste heated water from dying and other processes used in the plant and would normally go to waste.

Good answer.

I used 8.3 lbs /gallon and came up with around 4 million BTU/hr

It's not hard to work out the heat flow, as #3 and #4, but that doesn't tell you anything about the flow rate on the hot side, or the heat exchange area needed (which are interrelated).

I would suggest you approach the problem from the other side and calculate how much heat can be harvested from your 160F degrees flow. The flow rate on both sides, material and design of the heat exchanger will influence the rate of heat transfer and give you an idea of how much you will be cooling down one side and how much you will heat up the other side.

The simple calculations already given ignores the residence time inside the heat exchanger which is critical to the heat transfer. A lot more information is needed to know if heating up the water from 130F degrees to 15oF degrees is even feasible.

We already have the flow rate and temperature rise on the cold side, that gives the heat flow. The way I see it is the issue is finding the optimum design on the hot side, between large exchange area/low ΔT and small exchange area/high ΔT.