Preparing a Forced-air Wood Kiln

Here's a short video showing my wood kiln, which is almost ready to fire for the first time.  This is the first forced-air wood kiln I've ever seen.  Forced-air means that a fan is used to create the draft.  Normally a wood fired kiln does not use a fan, but instead relies on a tall chimney to create a suction or draft through the convection process of heat rising through the tall chimney.

The fire box is set slightly off-center (to the right) which was done to creat a swirling vortex.  This vortex extends the flame path through the firing space, providing more complete combustion and more even temperatures.

Initially this kiln was a gas-fired forced air kiln, built as a prototype under a grant I received from the New York State Energy Research & Development Authority (NYSERDA).  Originally it had 3 burners, each capable of producing 750,000 Btu per hour.  I built another conventional rectangular kiln of the same size, same wall thickness, same burners, etc., for the purpose of comparison.  My kiln proved to be 37% more efficient than the rectangular kiln, which is really quite an improvement.  This kiln is a downdraft, meaning that the hot flue gas vents at the bottom center of the kiln.

I adapted the original gas-fired design to a wood-fired configuration simply to see if it would work.   This is one big experiment: if it works well, it should fire faster than a conventional wood kiln.  A conventional wood firing usually takes around 3 days.  I'm hoping to cut that time substantially.  We'll see!

Hot Fluid Catalytic Beds

Hot fluid catalytic beds are used by industry to chemically process materials through heat, combustion and catalysis. One of the largest applications for hot fluid catalytic beds is by the fossil fuel industry, as employed by refineries which process crude oil into its component parts; from gasoline, kerosene, diesel, tar, to petroleum jelly, etc. Fluid Catalytic Cracking (FCC) is the dominant conversion process in petroleum refineries and the major contributor to “value added” in the refining process. Hot fluid catalytic beds are also used for creating fertilizers, cements and many other types of chemicals.

Here is a schematic image of a fluid bed used for cement production:

Here is a decent discussion of ‘cracking’, catalysis and fluid processes:

“The term “cracking” refers to the process through which large hydrocarbon molecules are split into smaller ones in order to obtain lighter hydrocarbons. This process requires very high temperatures and sometimes the use of a “catalyst”. In fact, there are different types of cracking. There are two types of cracking which have additional variations in the way they are implemented.

The first type of cracking is called “Thermal cracking”. It basically consists in heating the hydrocarbons until they reach high temperatures using also high pressures in some cases. This allows the hydrocarbons to break apart forming simpler hydrocarbons. The simple word “cracking” is often used to refer to this type of cracking as this is the oldest and most common type of cracking. However, thermal cracking can be achieved in different ways. There are three methods to implement thermal cracking:

• Steam - high temperature steam (1500 degrees Fahrenheit / 816 degrees Celsius) is used to break ethane, butane and naptha into ethylene and benzene, which are used to manufacture chemicals.

• Visbreaking - residual from the distillation tower is heated (900 degrees Fahrenheit / 482 degrees Celsius), cooled with gas oil and rapidly burned (flashed) in a distillation tower. This process reduces the viscosity of heavy weight oils and produces tar.

• Coking - residual from the distillation tower is heated to temperatures above 900 degrees Fahrenheit / 482 degrees Celsius until it cracks into heavy oil, gasoline and naphtha. When the process is done, a heavy, almost pure carbon residue is left (coke); the coke is cleaned from the cokers and sold.

The second type of cracking is called “Catalytic cracking” and it uses a catalyst to separate different hydrocarbons. This method of cracking generally uses zeolites as catalysts. Catalytic cracking can be also done through other catalyst such as aluminum hydrosilicate, bauxite and silica-alumina. As in the case of thermal cracking there are different methods to implement catalytic cracking:

• Fluid catalytic cracking- a hot, fluid catalyst (1000 degrees Fahrenheit / 538 degrees Celsius) cracks heavy gas oil into diesel oils and gasoline.

• Hydrocracking- similar to fluid catalytic cracking, but uses a different catalyst, lower temperatures, higher pressure, and hydrogen gas. It takes heavy oil and cracks it into gasoline and kerosene (jet fuel). Hydrocracking is basically a refining process that uses hydrogen and catalysts with relatively low temperatures and high pressures for converting middle boiling or residual material to high-octane gasoline, reformer charge stock, jet fuel, and/or high grade fuel oil. The process uses one or more catalysts, depending upon product output.

Once hydrocarbons have been cracked into smaller ones they pass through another fractional distillation column to be further distilled and to separate different components inside them.”

Here is a fluidized bed schematic for blast furnace metal production:

Catalysts are typically placed on an inert, chemically stable, refractory material. This is typically ceramic. Before the invention of the masonry system described here on this blog, these catalytic domes were made of custom ceramic parts which were precision fit to a specific location within a dome. This is time consuming and expensive.

Here's a photograph of the outside of a hot fluid catalytic bed reactor:

The masonry system I’ve been describing is ideal for applications such as hot fluid catalytic beds. All masonry units are interchangeable, they do not have to be custom cut, they do not have to be precision fit, and are much easier to assemble. Each masonry unit can be made with a through hole, to allow for hot gas to flow through the dome. Alternatively, the masonry units can be made of porous material, so that hot gas can also flow through the dome. Finally, the “dome” can be flipped upside-down, like a bowl. This is advantageous because in a dome the gas flow tends to be higher in the center of the dome; gas flow should ideally be equal across the surface of the dome, and inverted bowl helps to achieve this sort of flow.

This masonry system provides an improved method for constructing hot fluid catalytic beds for use in several fields of chemical processing industries.