Q. What is it supposed to be on the show?

A. An incinerator / furnace.

 
Q. Where is it supposed to be on the show?

A.  In an abandoned building in a very  dangerous neighborhood, somewhere in New York.

( Dexter remarks that rideshare drivers refused to go to that area, and even the NYPD were reluctant to go there. )

Q. When did we see it on the show?

A. Traditionally, Dexter disposes of his victims' bodies by dropping them into the ocean waters off Miami, from his boat, the Slice of Life.

But Dexter lost his boat when he drove into the hurricane at the end of the 8th season of the original Dexter.  And now that he's in New York, he has to find a new way of making those bodies disappear.

Back when he was living in Iron Lake (in Dexter: New Blood) he was forced to resort to using the town's incinerator when he returned to his killing ways. And now that he's in New York City, and still without a boat, he once again turns to using an incinerator as his means of getting rid of the evidence of his kills. 
 
He finds this new flaming furnace in what appears to be an abandoned factory, going there in the middle of the night.   

We see this incinerator twice in the first season of Resurrection:

In Episode 3, we get a full view of the location as Dexter drives towards the abandoned building after dark, to dispose of the remains of his first NYC victim: Ron Schmidt, the “Dark Passenger” killer.

In Episode 6 , Dexter revisits the furnace to burn the body of the first Gemini killer, after Gareth unexpectedly shows up in Dexter's apartment. 

6

Q. What is it actually in real life?

A. A former industrial building, now home to a design showroom.  

And from what I can tell, the neighborhood isn't particularly dangerous. It's just a former heavy industrial area down by the docks. Most of the brick buildings that used to make up this neighborhood have been torn down , but this building survives .  

 

Q. Where can I find it in real life?

A. You'll find this three-story brick building at 55 Ferris St,  in Brooklyn, NY, at the corner of Ferris & Wolcott.

That is located in a waterfront neighborhood known as Red Hook, which used to be a heavy industrial area and shipping port, and this old brick building is a remnant of that past. 

As Dexter drives towards the building at night in this scene, he is heading south down Ferris Street, just past Solomon Street.

Although the building appears to be abandoned when we see Dexter approaching it, it certainly is not vacant in real life.
 
But they needed us to think it was, in order for Dexter to get away with burning bodies in their furnace, so they added a few details such as bordered up windows, probably in post-production.

This building is actually now the studio and showroom of a company named PELLE, which creates a wonderful line of artistic lighting products (lights, lamps, chandeliers) inspired by natural elements like flowers, leaves  and bubbles. 
 
You can see a catalog with images of their unique work by clicking here and then scrolling down.
 

As for its history, the brick building at 55 Ferris Street in Brooklyn was built in 1882 (shortly after the Civil War) for the Lidgerwood Manufacturing Company, an iron foundry that made heavy machinery.

The brick building right next to it, at 43 Ferris, was built in 1899, and was it first the producer of bottling supplies, and later produced burglar proof locks, and then razor blades, before finally being bought by the E. R. Butler & Co., in 1997, the pre-eminent manufacturer of American period hardware.

You can read more about the history of the Red Hook here: https://www.erbutler.com/history/butler/red_hook_works
 
Since all of these businesses seem to be related to metalworking, odds are they had a foundry for melting the metal so they could pour it into molds. That’s probably why they have a tall chimney. But I have no idea whether such a furnace still exists, given its modern use. But I’m fairly certain that the furnace we see Dexter tossing body parts into is a studio set. The aerial view seen on the show doesn’t closely match what the Google Earth view.

Note that the actual building it is only seen in the first scene in episode 3, when Dexter is driving there to dispose of the Dark Passenger.

The second time he goes to the incinerator, to burn the body of the Gemini killer, we don't see the exterior, we only see the furnace inside, and most likely that is just a studio set.

 


 
Here is a matching StreetView of the building:


 
Here is an aerial photo of the location.  And here is a map link.