Improvements in Downdraught Furnaces.
Year: 1897

page_text: Date of Application, 3rd May, 1897
Complete Specification Loft, 3rd Feb., 1898-Accepted, 3rd May, 1898
PROVISIONAL SPECIFICATION,
Improvements in Downdraught Furnaces.
We, FORBES WADDELL, Gas Manager, Forfar, Forfarshire, ALEXANDER WADDELL,
Gas Manager, Broughty-Ferry, Forfarshire, and DAVID WADDELL, Tinsmith, 51, Shand
Street, Wishaw, Lanarkshire, Scotland, do hereby declare the nature of this invention
to be as follows:-
This invention consists of suitable means of supporting solid fuel in downdraught
furnaces and of maintaining fuel and combustion gases, where these gases are leaving
the solid fuel at such a temperature as may be required for complete combustion and
higher or lower as may be wanted for greater or less demands.
In water grates hitherto used in this type of furnace no means has been adopted to
maintain at a suitable temperature the fuel and combustion products where they are
in contact with the firebars.
We claim to be the first to appreciate the cause of failure of this type of fires, vis.—
the too great absorption of heat from the fuel lying on and the combustion gases
passing through between the firebars. This cooling of combustibles at the side of
fuel nearest chimney retards combustion and draught and in arrangements according
to our invention we have suitable means of raising and lowering at will the tempera-
tures of firegrate and fuel and gases in contact with it and thus have the rate and
intensity of combustion under control.
For suitable means of so controlling temperatures of firegrate and combustibles we
humbly crave a patent.
Many ways of controlling temperatures are available as for instance :-
(1) Passing water of certain temperature through firegrate made up of one or more
bent tubes and controlling the rate of flow through said tubes by suitable valves or by
regulating the pressure of water at inlets and outlets of such tubes.
(2) By having firebars in which water is maintained at a certain level with a steam
space or steam-way over the water surface. By having a means of raising one end
of bars the temperature of bars may be regulated by water comparatively cold, by
nascent steam or by superheated steam.
(3) In firegrates where the temperature of water cannot be kept high enough the
firebars are inade of such shape and materials of such conductiveness that the fuel
will be supported at a distance from water sufficient to keep it at a temperature
suitable for completing combustion.
(4) By any other suitable means.
No joined parts are exposed to the fire in our arrangements.
Suitable arrangements are made for utilising any heat absorbed by the water or
steam that modify the temperature of firebars.
FORBES WADDELL,
ALEXANDER WADDELL,
DAVID WADDELL.

page_text: 1
Improvements in Downdraught, Furnaces.
We, FORBES WADDELL, Gas Manager, Forfar, ALEXANDER WADDELL, Gas Manager,
Broughty-Ferry, and DAVID WADDELL, Tinsmith, Sband Street, Wishaw, all of
Scotland, do hereby declare the nature of this invention and in what manner the same
is to be performed, to be particularly described and ascertained in and by the
following statement :-
This invention consists of suitable means of supporting solid fuel on downdraught
grates and of maintaining fuel and combustion products leaving the fire at such a
temperature as is required to complete combustion and of controlling within certain
limits the intensity, and consequently the rate per square foot of grate area, of
combustion.
In water tube firebars for this type of furnace as hitherto adopted the temperatures
of the fuel and gases of combustion leaving the solid fuel have been dependent on
the efficiency of the water circulation without control and we claim to be the first to
appreciate and to remove the cause of failure of this type of furnace, viz., the too
great absorption by the water passing through firebars, of heat from the fuel and
from the products of combustion of the same just where the combustion products
leave the solid fuel. That absorption reduces the temperatures in the combustion
chamber and the results are incomplète combustion and reduced draught.
The accompanying drawing and the following describe our arrangement for bringing
about complete, therefore economical and smokeless combustion :-
The firegrate is preferably made up of hollow bars of steel or other suitable material
or materials of such a form as shown at A Figs. 2, 4, and 5, and B Fig. 2, having
dentals projecting outwards and upwards as shown in Figs. 4 and 5 just so far that
the fuel is supported on a surface the temperature of which is below the fusing point
of the material of which the upper surface of the bars is composed, but still at a
temperature sufficiently high to induce active or intense combustion.
The extent to which the dentals are projected is fixed according to the nature of
the material composing the bars and the temperature of the water or steam within
them. In this way a large area is obtained for the escape of the heat gases, and a
small area of cold bar surface exposed to heat products. The firebars are so shaped
longitudinally B Fig. 2, that the water passes from front to back and then from back
to front without traversing any joined part exposed to the heat of furnace.. We show
in Figs. 1 and 2 Fa main water inlet from water tank with fixed pressure to which
'the bars are connected by tubes R Fig. 1 and 2 through which water is passed through
bars shaped as at B Fig. 1 and 2, to back of grate thence along the return half of
bars to front and admitted to boiler through S Figs. 1 and 2. By valve Q Fig. 1 the
supply of water to bars is regulated so that it is evaporated slowly or rapidly
and consequently modifies the temperature and rate of combustion as may be
required..
Or as shown in Fig. 2 at A and Fig. 4 bars of the same section in single lengths
with ends at back closed have the front ends fixed in a proper manner to a
chest OY Fig. 1 and 2 passing across mouth of boiler flue. By a float valve P
Figs. 1, 2 and 3 or by other suitable means the water level is maintained at X
Figs. 1 and 4, so that the upper part of hollow of tube has its temperature modified
by nascent steam while the lower part of bar is covered by water at or near boiling
point. The water supplied to bars may be from the boiler and steam evaporated to
the boiler as shown or, it may be from an independent reservoir and to a hot well or
in any other suitable way. If water is supplied from and returned to boiler the chest
OY is made to communicate with MN. Figs. 1 and 3, which receives supply of water

page_text: from boiler through N and the steam generated enters boiler by valve M Figs. 1
and 3.
The flue front under bars is closed by means of suitable door which may have
openings for the supply of secondary air when that is required.
The grate is supported at front on suitable iron bearer and at back on a projecting
ledge, from a hanging bridge of brickwork L Fig. 2 and 3, the brickwork being built
so as as to prevent atmosphere or combustion products passing to chimney unless
through the firegrate.
A baffle brickwork bridge K Fig. 3 is built a short distance behind the hanging
bridge.
The baffle bridge has an opening closed by a hinged or portable door which can be
removed for the purpose of removing fine powdered ashes from bottom of flue.
The combustion field is by our own arrangement kept at a constantly high
temperature and the products of combustion complete and incomplete serve to keep
the banging bridge and baffle bridge brickwork at a temperature high enough to
bring about the combination of all partially consumed gases with the excess
atmosphere that is found in practise to be always present.
Having now particularly described and ascertained the nature of our said
invention, and in what manner the same is to be performed, we declare that what
we claim is :—
1. Hollow bars of similar section to that shown with no joined parts exposed
to heat of furnace.
2. The arrangements as shown for the controlling of the supply of water to
and consequently the temperature of firegrate surface and fuel on it and so
regulating the rate and temperature of combustion; or other suitable arrange-
ment for control of the aforesaid.
3. Forming the bars with dentals or other suitable projections whereby the open
area of grate surface, through which the heat gases pass, can be increased.
4. The ledge of brickwork on which firebars are supported is a help to completion
of combustion.
5. The brickwork bridge K Fig. 3 is a mixer of combustibles and an auxiliary
to combustion, and is a means of easily removing dust from flue.
Dated the 28th day of April 1898.
FORBES WADDELL,
ALEXANDER WADDELL,
DAVID WADDELL.