Whole timber firelog impregnated with combustible material

Disclosed is a new and improved firelog comprising whole timber to which highly combustible fuel is injected. The log further comprises a plurality of slits to enhance the combustion process. Various combustible fluids or combinations thereby may be used as fuel. Applicants further disclose a method of impregnating said combustible fuel into said firelog.

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This application claims priority from the provisional application with Ser. No. 60/671,667, which was filed on Apr. 15, 2005. The disclosure of that provisional application is incorporated herein by reference as if set out in full.


1. Field of the Invention

The invention relates to producing flammable compositions in the form of fireplace logs, designed to be used principally in household fireplaces, outdoor fire pits, chimneys etc. The invention utilizes whole timber logs impregnated with any suitable combustible material, to form a firelog for use either singly or in multiples. Also claimed are processes for producing said firelog.

2. General Background

Fireplaces are a commonly occurring household fixture built into homes for centuries, generally for the sole purpose of providing heat but sometimes used for cooking and even aesthetics. Indeed, the use of wood as a fuel source for home heat is as old as civilization itself. The traditional fuel source, firewood, is derived from trees or timber and provides a renewable energy resource provided the consumption rate is controlled to sustainable levels.

While wood, coal, or peat have traditionally been the primary fireplace fuel source, they are being replaced by other, alternative fuels such as natural gas, propane, fuel oil, and manufactured synthetic or artificial fireplace firelogs.

The amount of combustible energy in typical firewood is dependent upon the dryness of the wood. “Green” wood is roughly 10 MJ/kg, air-seasoned wood is approximately 16 MJ/kg and kiln dried wood is about 19 to 20 MJ/kg. The amount of energy per kilogram is largely independent upon wood variety. Thus, in a single cord of wood (128 cubic feet), the more dense the wood (i.e. oak, hard maple, hickory) the more energy the cord provides, and the less dense the wood (i.e. willow, aspen, or poplar), the less energy the cord provides. For reference coal provides generally between 25 and 35 MJ/kg.

In the past, techniques have been used to increase wood density, such as pelletizing the wood or compressing wood pulp into molded ‘logs’ of high density. These techniques increase the heat content per unit volume but do not necessarily change the heat content per unit weight.

Other techniques are now used to manufacture synthetic or artificial fireplace firelogs. These are generally produced by combining a particulate carrier material, usually of cellulosic origin, such as sawdust, with a combustible binder/fuel such as a mineral wax and then formed to size and shape through the use of in-line extruding equipment, or ram compaction equipment to form the firelog. Such synthetic firelogs can achieve up to 34 to 36 MJ/kg

Over the years there have also been several attempts to use a variety of agricultural and industrial waste products as the carrier material. Examples include sawdust splinters, cotton linter, charcoal powder, and other materials and techniques as described below:

U.S. Pat. No. 3,297,419 discloses the use of rice hulls or shredded paper as partial or total replacements for sawdust.

U.S. Pat. Nos. 3,843,336 and 3,880,611 disclose the use of reclaimed pulp and Northern Kraft paper beater stock respectively as sawdust substitutes.

U.S. Pat. No. 4,040,796 describes an artificial firelog comprising ground bark and peanut shells, further comprising a groove filled with gelled starter fuel along the length of the firelog.

U.S. Pat. No. 4,043,765 discloses the use of crushed nutshells, straw, paper pulp, and cotton waste as suitable substitutes for sawdust in an artificial firelog.

U.S. Pat. No. 4,120,666 discloses firelog formulations in which sawdust is substituted with shredded newsprint. As stated in the patent's abstract, “The logs are produced by continuously compacting shredded paper into one end of a compaction chamber, injecting hot molten wax into the compacted paper in the compaction chamber, cooling and hardening the wax, and continuously extruding finished logs from the opposite end of the compaction chamber with means for cutting the continuously extruded log into convenient lengths.”

U.S. Pat. No. 4,326,854 discloses the use of byproducts such as molasses, various waste oils or pitches and sulphite lye.

U.S. Pat. No. 4,333,738 discloses a synthetic firelog comprising wood fibers or sawdust, coal liquid, molasses and paraffin wax. The resulting mixture is poured into a mold and compressed to form a stable, solid, compacted mass.

U.S. Pat. Nos. 3,637,355 and 4,062,655 disclose a sawdust and wax firelog further comprising pyrogenic coloring matter distributed throughout the log mix, wherein the pyrogenic coloring matter produces flames of varying colors.

U.S. Pat. No. 5,496,384 discloses a synthetic firelog comprising primarily paper waste sludge material. This waste sludge material is mixed with a suitable wax and is pressed into a fireplace log having a plurality of longitudinally arranged bores that define passages for air to flow from one end to the other.

While each of the prior disclosed compositions would increase the energy density of the fireplace fuel beyond that of dried wood, the increased cost of mineral waxes and the decreasing availability of these waxes has led to an increased need to produce a high energy yield synthetic firelog not dependent upon wax.

An additional problem in the prior art is the high cost and complex production process currently involved in producing a synthetic firelog.

All these prior art disclosures for the manufacture of synthetic firelogs rely exclusively on the single technique of extrusion to compact and form the manufactured firelog. This manufacturing technique by definition restricts the choice of binder wax or blends of binder wax that are suitable to form and hold the form of extruded firelogs. Not all waxes will form compositions of saw dust/wax firelogs that will extrude adequately to form firelogs capable of subsequent handling during packing and distribution without collapse or fracturing. This manufacturing restriction therefore reduces the number of binder waxes that can be utilized and hence, restricts options for introducing cost reductions.


Applicants' disclosed invention advances the art beyond the above noted prior manufactured firelog and firelog manufacturing methods by using whole timber cut from logs into which a relatively weak structured liquid or wax is impregnated. Through using whole timber pieces, combustible materials may be used without need for a binder, thereby allowing relatively inexpensive combustible materials to be used.

A further object and advantage of the invention is that by the use of pieces of structurally strong whole timber, following impregnation with the additional combustible fuel material, the firelog remains whole and structurally sound during manufacture, packaging, transport, and even during the burn period of the product. In fact, during burning the firelog remains complete and does not spontaneously collapse or fall apart upon prodding. This avoids the possible safety problems of fire flare-up leading to chimney fire risk and/or excessive heat output should the log spontaneously collapse or be poked during the burn period, as is the case with conventional extruded synthetic firelogs based on sawdust and wax.

A further object of the invention is to produce energy enriched fireplace firelogs that are environmentally friendly by utilizing pieces of timber in combination with the optional use of non-fossil fuel-derived vegetable waxes or oils.

A still further object and advantage of the invention is a reduction in manufacturing cost by utilizing well-known and established technology such as is used in the impregnation of creosote preservative into fencing timber and utility poles.

A still further object of the invention is to provide a firelog that produces the crackling sound associated with the burning of natural timber.

A still further object and advantage of the invention is that through the use of highly porous timber types—such as but not restricted to, fast grown ‘Hem-fir’ it is possible to achieve impregnation levels greater than 50% by volume of combustible fuels such as molten vegetable waxes or oils.

Thus, the disclosed firelog provides all the advantages of traditional synthetic firelogs (that is, increased energy density above and beyond coal or wood alone, are easier to light, burn cleaner and for a known amount of time). Additional benefits above and beyond traditional synthetic firelogs include decreased cost of manufacturing and decreased maintenance and hence increased safety during burning.


FIG. 1 is a perspective view of a firelog.

FIG. 2 is an end view of the firelog, showing a longitudinal cross section taken along the lines 4-4.

FIG. 3 is a side view of the firelog, showing a cross section taken along the lines 6-6.

FIG. 4 is a longitudinal cross sectional view of the firelog taken along the line 4-4 in FIG. 2.

FIG. 5 is a bottom plan view of the firelog.

FIG. 6 is a cross sectional view taken along the line 6-6 in FIG. 3.


The applicants' have developed a new and improved firelog 1 that is based on a whole piece of timber, as most easily seen in FIG. 1. Although a shaped log is shown in the figures accompanying this application, the timber need not be pre-cut or shaped, and may even still retain the original bark during use and the impregnating process. For the purpose of this patent, an “upright” log shall be a log as shown in FIG. 6, where a flat bottom edge 4 is at the bottom.

Firelog 1, as shown in FIG. 1, is through a process to be described impregnated with additional combustible fuel additive. Various combustible fluids or combinations thereof may be used as fuel, including but not limited to alcohols (i.e. methanol (typical energy density: 56,000-65,000 BTUs/gallon), ethanol (76,000-82,000 BTUs/gallon), isopropanol), short chain hydrocarbons (i.e. hexane, heptane, gasolines (typical energy density: 110,000-120,000 BTUs/gallon) and diesel (typical energy density 130,000 BTUs/gallon)), long chain hydrocarbons (i.e. paraffin wax, microcrystalline wax, mineral or vegetable oils), natural waxes (i.e. long chain fatty alcohols and fatty acids or esters thereof), other grease, animal fats, or such combinations of the preceding components. In a preferred embodiment, tall oil pitch may be used after other components such as fatty acids and tocopherols are removed. It is important to note that any organic material in liquid form and that has a high BTU value may be used as fuel, but that certain fuels have advantages over others. The list of fuels above is thus presented for illustrative purposes only.

Because fireplaces are often used for the aesthetic value, choosing a material that burns with a yellow to orange flame is preferred, although any organic material can be used in liquid form.

Referring now to FIG. 1, a perspective view of the firelog 1 is shown. The firelog is in the shape of a generalized cylinder, a preferred embodiment of which is shown in FIGS. 1 and 2. The log may further comprise the flat bottom edge 4, which prevents the firelog from rolling due to center of gravity shifts occurring during the combustion process. The firelog surface 2 has the appearance of the surface of any ordinary log, substantially unchanged by the impregnating process. As previously indicated, the surface 2 may still comprise the bark from the original log, or, if the firelog 1 has been shaped from a larger piece of timber the surface 2 will simply be the surface newly exposed during the shaping process.

Referring now to FIG. 2, and end view of the firelog 1 is shown. The firelog 1 comprises two ends 3, one of which is most easily seen in FIG. 3. End 3 is substantially planar, allowing the firelog to be easily transportable, stackable, packagable, and to easily fit in standard household fireplaces.

The firelog further comprises a number of slits, as shown in the various figures. Along the flat bottom edge 4 are a plurality of bottom slits 8, as most easily seen in FIGS. 4 and 5.

The firelog also comprises a plurality of longitudinal slits extending centripetally from the outer edge of the firelog inward, each slip running the length of the firelog 1 as seen in FIGS. 4 and 5. In a preferred embodiment, the log comprises one top slit 5 and two additional 'side slits 7. The non-uniformity of top slit 5 may most easily be seen in the cross section shown in FIG. 4. From this Figure, the ramping ends 6 may be seen. The various slots are necessary to increase the log surface area allowing for a more even flame profile and an even burnout as the firelog is burned, thereby minimizing any unburned materials and charcoal residue. Additionally, upon initial ignition of the firelog, the time for the flame to fully engulf the firelog is reduced from more than 10 minutes to less than 5 minutes. This allows a more pleasing visual impression to be reached in less time.

Because the firelog is made from actual pieces of timber as opposed to synthetic firelogs, the natural crackling sound inherently produced during the combustion of natural timber remains. Synthetic firelogs in the past have resorted to adding artificial means to reproduce the sound created during the burning of the natural resins, voids, and density differentials in natural timber. (See firelogs disclosed in U.S. Pat. No. 6,602,306 to Scott et al. and U.S. Pat. No. 6,017,373 to Frisch).

In order to achieve the stated objectives of the invention, the firelog is processed as follows: The firelog may start as timber cut from trees specifically grown to a trunk diameter of approximately 3 to 7 inches, or from timber cut into approximately 12 to 18 inch long pieces of approximately 3 to 7 inches diameter, as shown in FIG. 1. The grading and trimming processes are not new in the art and may be easily performed by normal equipment found in timber processing plants. In an alternative embodiment, the timber can be cut from the preferred cylindrical shape into two substantially equal hemicylindrical pieces. The two pieces may be shipped and packaged together, and burned individually by an end user desiring a shorter burn time than would be provided by a full cylindrical firelog. Alternatively, multiple hemicylindrical pieces may be stacked the same as split cordwood.

Suitable types of timber include, but are not restricted to Western Hemlock, California Red Fir, Grand Fir, Noble Fir, Pacific Silver Fir, and White Fir, Douglass Fir, Yellow Fir, Balsa wood, Aspen, Willow and Western Cedar. Firewood cut from the fast growing hybrid polar tree is a preferred form of timber for processing according to the invention, however, any timber with a satisfactory level of porosity is acceptable.

Slits are then carved into the timber as shown in FIG. 1. These various slits may be easily carved with a circular saw as is well known in the art of woodworking. The ramping ends 6 of top slit 5 may also be easily shaped during this same process. Ideally, top slit 5 ramps up toward the surface 2 of the firelog at approximately 1 inch from each end, as is best seen in the cross section shown in FIG. 4.

Before the fuel is impregnated into the firelog during processing, the timber must be dried to near zero moisture content, thereby maximizing fuel loading. This is done by a number of means including kiln drying or by live steam heating followed by a low torr vacuum for 1 to 24 hours to vacuum dry the timber. A vacuum of approximately 10−8 torr and up to 1.5×10−8 will speed removal of residual water from the timber, while a weaker vacuum will require additional time.

Once the timber is dried to desired levels, the timber is placed into a treatment chamber, which is to be filled with impregnating fluid. Preferably, one chamber may be used for both the drying and impregnation phase of the process, thereby decreasing overall processing. The timber is preferably placed in a frame that will secure the timber in a position below the fluid level of the impregnating fluid.

While still remaining under a strong vacuum, the chamber is flooded with molten fuel component materials at a temperature high enough to prevent the wax ‘freezing’ into the surface of the logs and thus preventing further impregnation once the vacuum is released and pressure applied. While still maintaining the molten characteristics of the fuel components, the vacuum is released and pressure is increased inside the system up to 250 lbf/in2. This high pressure is maintained for a period long enough to ensure maximum loading of fuel component materials into the firelog. The ramping ends 6 of the firelog helps ensure that slot 5 does not close up due to the high temperatures involved with the impregnating process. Once a desired amount of fuel component materials are stored in the firelog, the system pressure is then released and excess fluid is pumped back to the holding tank for loading of additional firelogs. In an alternative method of fuel impregnation, the firelog may be submerged in said fuel at ambient atmospheric pressure and temperature, thereby reducing cost of product, but increasing time of production.

Before packaging, excess fuel is allowed to drain from the treated firelog. Alternatively, a vacuum may be applied to quickly dry firelog surface 2.

As described above, any organic material in liquid form and that has a high BTU value may be used as fuel, but certain fuels have advantages over others. Preferred fuel component materials are molten vegetable oils or waxes or combinations of vegetable oils and waxes derived from palm oils and fatty acids or fatty alcohols, or soy oils and fatty acids or fatty alcohols.

After processing, the firelog in a preferred embodiment will contain by volume 15-99 part of timber impregnated with 1-85 parts additional combustible ‘fuel’. More preferably, the log will comprise 35 to 60 parts of timber impregnated with 40 to 65 parts additional combustible ‘fuel’; and in the most preferred embodiment will comprise preferably 40 to 60 parts timber with 40 to 60 parts additional combustible ‘fuel’. A second means for quantifying the amount of fuel update by any particular piece of timber as a ratio of the amount of liquid lost by the timber during the drying process. In a preferred embodiment of the invention the ratio of fuel impregnated to liquid removed is at least 9:10, and less preferably at least 7:10.

The cost-reducing objective of applicant's invention is met because the treatment of timber in this fashion is relatively inexpensive. Post treatment, the energy content of the firelogs is approximately 37 MJ/Kg. Relative to pre-treatment weight, the log increases in weight dramatically, and in a most preferred embodiment, by approximately 95% to 105%. Depending on the type of timber used, other weight gains may be expected.

In an alternative embodiment of the invention (not shown) the above processes are applied to small chips of wood. The process is nearly the same but during the submersion and impregnation process, a small mesh screen is needed to secure the wood chips under the liquid level.

In additional alternative embodiment of the invention (not shown) the treated firelog is enclosed in bag-like flammable casing ignitable from a common burning matchstick. The bag is preferably made from paper, cardboard, or other fibrous materials, and comprises a strip of material incapable of combustion at the temperatures associated burning the firelog. Thus, in a complete burn of said firelog and casing, the only material left is charcoal from the wood and unburned strip. Preferably, the strip comprises tinfoil but the strip may comprise a plate like structure with cupping edges. Preferably, the bag is substantially sealed

The positioning of the strip is to place it at the bottom portion of the casing. That is, the strip runs longitudinally under the log and in a preferred embodiment slightly cups up around the edges of the log by a small amount.. The purpose of the strip is to ease cleanup of charcoal that remains after the firelog is burned. Because the strip cups up around the bottom edges of the firelog, falling charcoal is largely maintained on the strip. A user may then simply pick up and dispose the strip, taking with it the ashes and charcoal from the burned firelog. The cupping edges of the strip must not extend any higher than the side groves when the log is positioned upright as is shown in FIG. 6.

The strip may either be affixed to the inside or outside of the bottom of the bag, or may be laminated into the bag material as is commonly known in the art of lamination. In an alternative method of preserving an unburned cup-shaped portion of the packaging, the bottom portion of the bag may be treated with a fire retardant. Thus, after a complete burn, a user may clean up remaining charcoal and ash by simply picking up the cup-shaped unburned portion of the firelog packaging.


1. A whole timber firelog comprising:

a. a log-shaped combustible body comprising: i. timber and one or more fuel additives in a ratio of between 30:70 and 70:30 wherein said fuel additives are chosen from the group consisting of alcohols, short chain hydrocarbons, long chain hydrocarbons, natural waxes and tall oil pitch; ii. a flat bottom-edge; and iii. a plurality of longitudinal slits extending centripetally wherein one longitudinal slit has ramping ends;
b. wherein said log-shaped combustible body: i. has at least 35 MJ/kg potential energy; and ii. produces a crackling sound when burned.

2. The whole timber firelog of claim 1 wherein said fuel additives are in a ratio of between 40:60 and 60:40.

3. The whole timber firelog of claim 1 wherein said log-shaped combustible body is impregnated with said fuel additives.

4. The whole timber firelog of claim 1 wherein said fuel additives consists of tall oil pitch.

5. The whole timber firelog of claim 1 wherein said fuel additives consists of one or more fats.

6. The whole timber firelog of claim 1 wherein said fuel additives have an energy density of at least 56,000 BTUs per gallon.

7. The whole timber firelog of claim 1 wherein said timber is taken from a hybrid poplar.

8. The whole timber firelog of claim 1 wherein said log has a volume, and wherein said fuel additives impregnated occupy between 35% and 85% of said volume.

9. The whole timber firelog of claim 1 wherein said potential energy is at least 37 MJ/kg.

10. A method of manufacturing a whole timber firelog comprising:

a. cutting a log to a length of less than two feet wherein said log;
b. carving a plurality of longitudinal slits into said log;
c. removing moisture from said log;
d. pressure treating said log in a treatment chamber wherein one or more fuel additives are absorbed into said log;
e. removing said log from said treatment chamber; and
f. draining excess said fuel additives from said firelog.

11. The method of claim 10 wherein:

a. said fuel additives are absorbed while said log is submerged in said fuel additives; and
b. said chamber is maintained at ambient pressure and temperature.

12. The method of claim 10 wherein said fuel additives are absorbed through pressure treatment.

13. The method of claim 12 wherein said removing nearly all moisture is accomplished through use of a vacuum chamber at a maximum 1.5×10−8 torr.

14. The method of claim 12 wherein said fuel additives have an energy density of at least 56,000 BTUs per gallon.

15. The method of claim 10 wherein the ratio of fuel additives absorbed into said log to moisture removed from said log is at least 7:10.

16. The method of claim 15 wherein said removing nearly all moisture is accomplished through use of a vacuum chamber at a maximum 1.5×10−8 torr.

17. The method of claim 15 wherein said fuel additives have an energy density of at least 56,000 BTUs per gallon.

18. A combustible fuel additive-impregnated wood chip comprising:

a. a wood chip comprising timber;
b. an amount of a plurality of fuel additives of at least 30% by weight of said wood chip; and
c. wherein said wood chip: i. produces a crackling sound when burned; and ii. has at least 35 MJ/kg potential energy;

19. The combustible fuel additive-impregnated wood chip of claim 18 wherein said amount of fuel additives is at least 50%.

20. The combustible fuel additive-impregnated wood chip of claim 18 wherein said fuel additives comprises a plurality of fats.

21. A firelog package for containing and igniting a firelog comprising:

a. a substantially sealed paper-like bag having a bottom portion further comprising a fire-retardant portion.

22. The firelog package of claim 21 wherein said fire retardant portion comprises a metal strip.

23. The firelog package of claim 22 wherein said metal strip comprises foil.

Patent History
Publication number: 20060230673
Type: Application
Filed: Apr 15, 2006
Publication Date: Oct 19, 2006
Inventors: Eric Barford (Magnolia, TX), Prodromos Stephanos (Walnut Creek, CA)
Application Number: 11/404,394
Current U.S. Class: 44/535.000
International Classification: C10L 11/00 (20060101);