Industrial Combustion and Emissions

[jmog]

I have spent 20+ years as a ”combustion engineer” working on everything from industrial food baking ovens to steel and glass melting furnaces.

Typically I center around emissions (NOx, SOx, CO, and CO2) reductions and efficiency gains.

This has also brought about “side” knowledge about car emissions and the EV car market as I have done design and melting/refining work on the heat treat and melting furnaces for the rare earth metals used in EV batter and EV magnetic motor components.

So if you want to know anything about combustion from a camp fire to a house furnace to steel melting plant, here I am.

20+ years actual experience
BS in Chemical Engineering
BS in Applied Mathematics
MS in Chemical Engineering

 

[D4fan]

Took me a second on the food commercial ovens. The last thing I want In my ovens is combustion. They are electric.

Here is a basic question that has puzzled me over the years. A gallon of propane always has 91,502 btu available potentially but a therm (100 cubic feet) of natural gas varies widely in available energy. What causes the variation and what are the extremes in terms of available energy?

Now for a combustion question, had a new 94% efficient furnace put in this year. They ran the exhaust in 3" PVC to the outside, but they simply put a 2" elbow at the intake and rather than piping air in from outside, it draws air from the basement for combustion. Which is more efficient, ambient outside air for combustion or 65 degree Fahrenheit basement air?

 

[jmog]

1. Because propane is just that, basically pure propane. Natural gas is a mixture of gases that greatly varies from region to region. Its main component is methane (usually 85-95%) but it also contains butane, propane, carbon dioxide, nitrogen, etc in varying amounts. This variability in what comes out of the ground in various parts of the planet is why the energy value of NG also varies, because methane has less BTUs than butane or propane. NG can vary from say 900 to 1100 BTU/cu ft but averages about 1030.

2. Basement air vs outside air doesn’t really change efficiency. The inside air is better climate controlled (read closer to same temperature year round) which makes the air to fuel ratio more consistent than if you pulled from outside air since air expands as it heats up and contracts as it cools down. A consistent air to fuel ratio is key to make sure you don’t go excessively rich (carbon build up on burner) to or lean (inefficient).

3. Its 2” inlet and 3“ outlet because the combustion process with natural gas creates more volume of gases (not more mass obviously) in the chemical reaction and the exhaust is hotter than the cold air inlet so more gases and hotter so the piping needs to be larger to get a good draft with less pressure losses.

 

[jmog]

Took me a second on the food commercial ovens. The last thing I want In my ovens is combustion. They are electric.

Good news for you, most industrial food baking ovens are indirectly fired/heated. This means the burner/fire is inside of a tube and the tube heats/cooks the food (bread, pretzels, whatever) so the gas products of combustion aren’t in the same chamber as the food.

This is not all, but definitely most.

 

[IVCguy]

We have a rendering plant about 1 1/2 miles NW of our home as the crow flies. Dead animals are taken there from farms and animal parts from area processing plants. From there, the animals are cooked down and used for animal byproducts. This is a "stinky" process.

For years the plant just cranked out a foul-smelling smoke. I'm talking about make-you-gag type of odor. We only smelled it maybe once a month because the prevailing winds don't blow in our direction very often, but if you had an outdoor get together planned, that's when we would get it - particularly on days with a low cloud ceiling, high humidity, and winds NW to SE.

I was confused about why this was happening because I am aware of rendering plants located in towns and you never smell a thing.

Many people complained to county and state officials. I complained directly to the company and was told, "that's the smell of money". Lol. I was told that the plant was regularly monitored and inspected by the Ohio EPA.

In recent years, say the last 10, we never smell anything M-F 9AM to 5PM, but we occasionally get a strong dose in the evenings, overnight, or on the weekends.

I was told the plant is required to use "scrubbers" on their smokestack, and these scrubbers are what prevents the bad odors. I was also told that those scrubbers are expensive to operate. Given the pattern of when we smell bad odors, it appears that the company is not using them from 5:01PM-8/9AM M-F or F 5:01PM to 8/9AM Mon.

But what can you tell me about these kinds of emissions, what the regs are, and how the emissions are mitigated?

 

[jmog]

We have a rendering plant about 1 1/2 miles NW of our home as the crow flies. Dead animals are taken there from farms and animal parts from area processing plants. From there, the animals are cooked down and used for animal byproducts. This is a "stinky" process.

For years the plant just cranked out a foul-smelling smoke. I'm talking about make-you-gag type of odor. We only smelled it maybe once a month because the prevailing winds don't blow in our direction very often, but if you had an outdoor get together planned, that's when we would get it - particularly on days with a low cloud ceiling, high humidity, and winds NW to SE.

I was confused about why this was happening because I am aware of rendering plants located in towns and you never smell a thing.

Many people complained to county and state officials. I complained directly to the company and was told, "that's the smell of money". Lol. I was told that the plant was regularly monitored and inspected by the Ohio EPA.

In recent years, say the last 10, we never smell anything M-F 9AM to 5PM, but we occasionally get a strong dose in the evenings, overnight, or on the weekends.

I was told the plant is required to use "scrubbers" on their smokestack, and these scrubbers are what prevents the bad odors. I was also told that those scrubbers are expensive to operate. Given the pattern of when we smell bad odors, it appears that the company is not using them from 5:01PM-8/9AM M-F or F 5:01PM to 8/9AM Mon.

But what can you tell me about these kinds of emissions, what the regs are, and how the emissions are mitigated?

Any type of animal rendering plant, their main emissions are VOCs (volatile organic chemicals).

The VOCs specific to this process usually organic sulfides or disulfides.

Think something like full sulfur diesel (best common chemical I can compare it to).

sulfur compounds almost always smell bad, the plants would have a TO (thermal oxidizer) to burn the VOCs up before they go into the atmosphere.

This process would turn any sulfur atom in the VOCs to “SOx” or sulfur oxides (SO2 and SO3).

SOx is also bad for the environment so the next step is “scrubbers” that typically use a calcium based molecule to covert SOx into CaSO4, which is gypsum.

That process is the same that coal fired power plants use and is why you will normally see a drywall plant right down the road of a coal fired power plant, cheap artificial gypsum raw material they don’t have to dig out of a mine shaft.

The sulfurs are what you are smelling, and most likely the infrequency you smell it now is due to only when either the TO or scrubber goes down. Typically they only have so much time (minutes or hour’s depending on how bad their chemical is) to fix the TO or scrubber before shutting the plant down completely.

Some chemical plants have to shut down immediately if their TO goes down for instance. It sounds like the rendering plant near you has some “time” to get it working before shutting down. That is usually based around the permissible emission limits for a year and if it will make them go over said limits.

 

[gneiss rocks]

We have a rendering plant about 1 1/2 miles NW of our home as the crow flies. Dead animals are taken there from farms and animal parts from area processing plants. From there, the animals are cooked down and used for animal byproducts. This is a "stinky" process.

For years the plant just cranked out a foul-smelling smoke. I'm talking about make-you-gag type of odor. We only smelled it maybe once a month because the prevailing winds don't blow in our direction very often, but if you had an outdoor get together planned, that's when we would get it - particularly on days with a low cloud ceiling, high humidity, and winds NW to SE.

I was confused about why this was happening because I am aware of rendering plants located in towns and you never smell a thing.

Many people complained to county and state officials. I complained directly to the company and was told, "that's the smell of money". Lol. I was told that the plant was regularly monitored and inspected by the Ohio EPA.

In recent years, say the last 10, we never smell anything M-F 9AM to 5PM, but we occasionally get a strong dose in the evenings, overnight, or on the weekends.

I was told the plant is required to use "scrubbers" on their smokestack, and these scrubbers are what prevents the bad odors. I was also told that those scrubbers are expensive to operate. Given the pattern of when we smell bad odors, it appears that the company is not using them from 5:01PM-8/9AM M-F or F 5:01PM to 8/9AM Mon.

But what can you tell me about these kinds of emissions, what the regs are, and how the emissions are mitigated?

Yikes, get one of those black death/plague doctors mask, fill botanical herbs... you may look like a freaky man bird and scare the heck out of the neighbor kids but it should help.

 

[IVCguy]

Yikes, get one of those black death/plague doctors mask, fill botanical herbs... you may look like a freaky man bird and scare the heck out of the neighbor kids but it should help.

I already scare the heck out of the neighbor kids with my normal appearance.

Weird thing is I'm always good for smarties, a piece of bubble gum, or money so despite my ogre-like appearance, I am pretty popular in the neighborhood with the kids. Lol