Are there any chemical additives to eliminate soot deposit on heat exchanger?

If your burner is properly set up, it’s an easy clean, not a headache at all.
And almost never any soot on a modern appliance.

In the 1970s The oil company where I learned the trade had a "Clean Burning Oil Heat" campaign in order to compete with the Natural Gas Utility advertisements about "Clean Burning Natural GAS". Part of this campaign included 3 chemicals. The fuel oil additive APC-30, a liquid soot remover that was actually pumped thru the fuel pump, and a degreaser that was used like Spray 9 or Fantastic to clean the equipment after the annual tune-up to make the furnace/boiler Jacket look like new. I remember using the fittings with clear hoses to connect the 1 gallon metal can full of soot remover to the fuel pump. Operate burner for 10 minutes. Watch the soot actually burn off the surface of the HX. Then the white residue that was left could be brushed away with a soft brush, and left in the bottom of the heat exchanger.

This was great to use if the boiler had 3/8" coating or more of the fluffy soot. (similar to the soot in your photo) Not so much on the scale and other deposits normally found on a HX that was normally found when the oil burner was set up to burn clean in the first place.

As oil heat customers converted to gas heat in the 70s, 80, and 90, and the clean burning flame retention burners like Carlin and Beckett became more popular, there was less soot to remove and the company that marketed the products went out of business. So there is a liquid chemical that can be pumped thru the fuel pump and nozzle that will remove that soot, I just don't know where to get it, or even if it is available for retail use.

Combining a Pressure-Fired Beckett NX Oil Burner with a Weil-McLain Three-Pass Boiler yields zero soot and minimal fly ash, dependent upon fuel quality. We do "annuals" every two/three years and have tested up to five years. Ultimately the limit is fuel quality/filter service.
When I began with my Dad 67 years ago, we were nicknamed "Soot Chasers" ..... no more!

cowdog said:

Soot deposit on heat exchanger is a headache for any oil heating appliance. Are there any chemicals that can stop soot from forming or depositing? Can we add this chemical to the fuel, or spray it periodically to clean out soot on heat exchanging surfaces? Is it possible to have a motor-driven scraper to scrape the heat exchanging surfaces periodically? Why don't household oil heaters use it?

A properly sized, installed and set up with a combustion analyzer doesn’t need one. 

cowdog said:

pecmsg said:

A properly sized, installed and set up with a combustion analyzer doesn’t need one. 

It's a negotiation between fuel and equipment. Improvement on equipment will be "eaten up" by using a dirtier fuel.

It's just like computer software become bloated and inefficient while computer hardware and networks become faster.

It will need one if they switch from oil to waste oil, pyrolysis oil or emulsified #6 fuel oil. Because there are demand, we need to develop universal burners and wide compatible cleaning chemicals and protocols.

Are you building something to use waste oil for an industrial piece of equipment or are you trying to piece all of this together to heat your house?

Necessity is the mother of invention!. Currently there is no need to mass produce a motorized soot removal apparatus.@cowdog may be on to something though.  Once we are regulated into a fossil fuel free world, there will be a black market for ant type of fuel that will keep the poor folks that still have coal converted boilers and furnaces in their basement.   Since the fuel quality won’t be regulated, you never know what’s gonna end up on the walls of those heat exchangers. Someone who invents  a cleaning device for sooty heat exchangers could make a fortune.