Heat Recovery – is it “Free Money”?

I began my career at Alloy in 1990, and by that time most packer-renderers, where the rendering plant and the kill facility were on the same property, already had heat recovery systems.  I recall reviewing internal Alloy files to review system pricing and found that the real heyday for these systems was the late 1970’s to the mid 1980’s.  We still do a number of heat recovery projects each year, but the majority of them are heat exchangers that just need replacement.  In Central and South America there are a number of companies that do not have heat recovery systems, but should.

So the question is: do heat recovery systems equate to “free money”?  The answer is yes, it truly is free money, if you have a need for hot water and do not already have heat recovery.

How does it work and why would I claim it is free money?

The main piece of equipment in the heat recovery system is a shell and tube condenser.  This piece can sometimes be called a condenser, a heat exchanger, or a shell and tube condenser but it really is the same piece of equipment no matter what you call it.  The vapor (evaporated water from the raw product) must be condensed in virtually all plants.  Even in less regulated countries, there are very few renderers who can discharge vapor directly to atmosphere.  Many independent renderers who do not have use for hot water will utilize an air condenser, a barometric condenser, or a shell and tube condenser with a cooling tower.  The down side to all of these approaches is that they cost you money to operate.

With a heat recovery system, you claim the heat from the rendering vapor and literally heat the water for free.  Starting with potable cold water sent to the heat exchanger after providing the cool water to condense vapors and keep the rendering system under vacuum, what exits is potable hot water.  In a kill facility, you would need to pay money to heat cold water for sanitation wash down, carcass wash, scalding, for your boilers, etc.  That is why I claim it truly is free money.  Every plant in the United States that has a kill plant and rendering on the same property utilizes heat recovery and the savings is huge.  The only issue I have ever seen is that some plants have a hard time utilizing all of the free hot water they generate.

There is a fair amount of math involved to understand how much money is saved but I will do my best to give an accurate example that is straightforward.

For my example I will use 15,000 pounds of vapor per hour for 20 hours per day (typical rendering day for many plants).  15,000 pounds would be a 200 U continuous cooker, or about 7 batch cookers.

Each pound of vapor contains 1000 BTU’s

Here is the math and in the case of heat recovery theory and reality come together so this is real savings.

Heat available per hour 15,000 LB/HR * 1,000 BTU/LB = 15,000,000 BTU/HR

Heat available per day = 15,000,000 BTU/HR * 20 HR/Day = 300,000,000 BTU/Day

Gas cost assumes 3.5 per MCF (1,000,000 BTU)

Gas savings 300,000,000 BTU/1,000,000 BTU/MCF = 300 MCF per day

Almost all plants use a boiler to generate steam which is then used in a pick heater or other device if free hot water is not available.  Boilers are about 80% efficient on average.

Boiler correction = 300/.8 = 375 MCF per day saved

375 MCF * 3.50 per MCF = $1,312 saved per day

$1,312 per day * 260 day per year = $341,250 saved annually.

Plants that use Bunker C (fuel oil #6) in boilers:

For the accounts I have visited outside the US it is hit and miss regarding the availability of natural gas.  Many accounts still burn bunker C in their boilers.  Bunker C is far more expensive than natural gas so the savings is even greater in utilizing a heat recovery system.

The average cost for Bunker C in Central America is $2.25 per US gallon and that is low compared to historical averages.  One gallon of Bunker C has 151,000 BTU’s

So using the same calculations and assumptions as above and just changing from natural gas to bunker C the savings is as follows:

300,000,000 BTU per day saved / 151,000 BTU per gallon bunker C = 1986 gallon per day saved

Boiler correction = 1986/.8 = 2,483 gallons bunker C saved

2,483 Gallons * $2.25 per gallon = $5,586 saved per day

$5,586 per day * 260 day per year = $1,452,000.00 saved annually.

Note that most US plants are much bigger than 15,000 pounds per hour of vapor but most Central American plant are much smaller than 15,000 pounds per hour of vapor.  So call an Alloy applications engineer to see how much you could save.  Who would refuse “free money”?