GB2523790A

GB2523790A - Improvements to wood pellet boilers

Info

Publication number: GB2523790A
Application number: GB1403879.8A
Authority: GB
Inventors: Declan John Crosse
Original assignee: SUIRVALE DEVELOPMENTS Ltd TA WOOD ENERGY SOLUTIONS
Current assignee: SUIRVALE DEVELOPMENTS Ltd TA WOOD ENERGY SOLUTIONS
Priority date: 2014-03-05
Filing date: 2014-03-05
Publication date: 2015-09-09
Anticipated expiration: 2034-03-05
Also published as: GB2518933B; GB2523790B; IE20150051A1; GB2518933A; GB201403879D0; GB201411564D0; IE20150050A1

Abstract

A biomass boiler comprises a housing having an integrated hopper (120, fig 9) for wood pellets, a means of igniting the wood pellets, a burner pot (144, fig 11) having a cleaning means 154, and a heat exchanger 200 having a further cleaning means (205, fig 31). The boiler may comprise a water circulation pump, water pressure sensor, an air vent and a pressure relief valve. The burner pot may comprise primary (145, fig 13) and secondary (157) combustion zones having a plurality of air holes (147) and may be removable from a combustion chamber (140). The secondary zone may comprise a narrowing knuckle region (156) creating a venturi effect. Internal surfaces of an upper region (180, fig 30) of the combustion chamber may have a profile (182) to form a vortex of hot gases. A removable baffle 185 may be mounted in the combustion chamber and hangs down under its own weight against a side of the combustion chamber to aid in heat transfer to the heat exchanger. The heat exchanger is a secondary pass heat exchanger comprising of one or more tubes having a turbulator (205) operated by a motor (128) driven crank mechanism (129) for the cleaning.

Description

IMPROVEMENTS TO WOOD PELLET BOILERS

The present invention relates to boilers which use biomass as fuel and more particularly to The present invention provides an external biomass boiler comprising a slimline housing, one wall of which is adapted to fit adjacent an existing structure, a self-cleaning and automatic ignition wood pellet boiler, an integrated hopper for wood pellets; a burner pot having cleaning means and a secondary pass heat exchanger having separate cleaning means.

Advantageously, the boiler further comprises an integrated circulation pump, a water pressure sensor, an air vent and a pressure relief valve.

Ideally, the burner pot includes a primary combustion zone and a secondary combustion zone, a plurality of air holes in said combustion zones and a narrow knuckle region in the secondary combustion zone adapted to create a Venturi effect and improved secondary combustion.

Conveniently, in which the burner pot holder is provided in the combustion chamber of the boiler and into which the burner pot is removably engageable, the burner pot holder being adapted to receive combustion air provided by a combustion fan and form a cavity between the surfaces of the burner pot and the combustion chamber.

Preferably, internal surfaces of the upper region of the combustion chamber are adapted to receive the hot gases from the combustion of the fuel and retain the gases for a period of time, the profile of the internal surfaces of the upper region of the combustion chamber forming a vortex allowing the hot gases to contact as much of the heat exchanger suifaces as possible.

The boiler is an external wood pellet (biomass) boiler and is a shallow fit unit which can be located externally incorporating a 15 or 18kW self-cleaning and fully automatic wood pellet boiler, integrated fuel hopper, pneumatically cleanable burner pot and mechanically cleanable secondary pass of the heat exchanger. It is also fitted with an integrated circulation pump, water pressure sensor, air vent and pressure relief valve. Efficiency is greater than or equal to 89%. The product is designed so that it can be sited directly against a wall without any requirement to access the rear of the product for service or maintenance. The plinth on which the product rests is generally on a footpath with the back wall of the unit against a wall. It is fully serviceable from the front. The unit depth is <600mm and standard footpaths vary between 1000-1200mm wide leaving adequate walkway space in front of the unit. In other prior art products, where access is required to all sides for servicing, alterations are required to footpaths, etc. to satisfy the space criteria of local authorities.

Combustion is supported by a combustion fan which introduces air into the burner pot holder where it is allowed to exit into the burner pot through air holes. Regulation of underpressure in the combustion chamber is by means of an exhaust fan whose speed is controlled from information received from a vacuum pressure sensor which samples draft in the combustion chamber. This dual fan system with separate control regulation is unique in a pot type drop feed burner arrangement where the fuel in introduced by means of a drop feed from above the burner pot. The regulation of the exhaust fan ensures that heat transfer or burn back does not occur towards the fuel supply. Safety interlocks are in place within the digital control system to put the system operation into a safety condition in the event of failure of the exhaust fan or combustion fan.

The invention will hereinafter be more particularly described with reference to the accompanying drawings which show, by way of example only, one embodiment of a wood pellet boiler according to the invention. In the drawings: Figure 1 is a side view of the complete boiler; Figure 2 is a front view of the complete boiler; Figure 3 is a view from the other side of the complete boiler; Figure 4 is a plan view of the complete boiler; Figure 5 is a side view of the boiler with the outer panels removed; Figure 6 is a front view of the boiler with the outer panels removed; Figure 7 is a view of the other side of the boiler with the outer panels removed; Figure 8 is a plan view of the boiler with the outer panels removed; Figure 9 is a perspective view of the boiler from the front and one side with the outer panels removed; Figure 10 is a perspective view of the boiler as shown in Figure 9 but from the front and the other side; Figure 11 is a perspective view of the boiler as shown in Figure 9 with inner panels removed showing a burner pot and a burner pot holder encircled; Figure 12 is an enlarged view of the encircled view of Figure 11; Figure 13 is a perspective view of the burner pot; Figure 14 is a front view of the burner pot; Figure 15 is a side view of the burner pot; Figure 16 is a cross-sectional view of the burner pot along A-A of Figure 14; Figure 17 is a plan view of the burner pot; Figure 18 is a view from the other side of the burner pot; Figure 19 is a cross-sectional side view of the burner pot along A-A of Figure 18; Figure 20 is a perspective view from one side and the front of the burner pot holder and burner pot; Figure 21 is a perspective view from the other side and the rear of the burner pot holder and burner pot; Figure 22 is a front view of the holder and burner pot and Figure 23 is a side view; Figure 24 is a front view of the boiler as shown in Figure 11; Figure 25 is a cross-sectional end view along A-A of Figure 24 showing a hanging baffle in position; Figure 26 is a perspective view of the hanging baffle; Figure 27 is a cross-sectional side view along B-B of Figure 25; Figure 28 is an enlarged view of the area encircled in Figure 27; Figure 29 is an end view of the boiler; Figure 30 is a cross-sectional side view of the boiler along A-A of Figure 29 showing the path of the flue gases and a cross-section through an exhaust pipe having a turbulator within the pipe; Figure 31 is a side view of a portion of a turbulator; and Figure 32 is an enlarged view of the portion encircled in Figure 31.

Referring to the drawings and initially to Figures ito 4, the boiler 100 of the invention is of slim line rectangular shape and is finished with a series of outer panels, namely a front panel 101, a rear panel 102, a first side panel 103 and a second side panel 104 and a top cover 105. A flue pipe 106, of whatever required length, extends upwardly from the top cover 105.

Referring to Figures 5 to 10, the boiler includes a combustion fan 102 and an exhaust fan 104 at either side of the combustion chamber 140 which has a separate door 105 for access purposes and a cleaning access door 106 at the side of the boiler. The hopper includes a fuel delivery auger 122 located in a delivery pipe 124 and operated by an auger motor 125. A safety grid 126 is provided at the top of the hopper to prevent a user coming into contact with the auger 122 while the hopper is being filled with fuel. A flue outlet 127 extends from the combustion chamber. The flue pipe 106 is attached to the flue outlet 127. Mounted on top of the combustion chamber is heat exchanger cleaning motor 128 which operates cleaning crank mechanism 129. Associated with the door 105 is door safety switch 131 which activates when the door is open and prevents ignition of the burner. Located above the safety switch 131 is vacuum sensor 133 which also prevents ignition if there is not sufficient vacuum for ignition and exhaust purposes.

In the remainder of the drawings, the outer panels are removed for clarity, and the boiler 100 includes three main sections, a hopper 120 for biomass material, a combustion chamber 140 and a water filled panel heat exchanger 160 for harnessing the heat generated by the fuel burnt in the combustion chamber 140. Beneath the combustion chamber 140 and heat exchanger 160 is an ash pan 170 for collecting ashes from the combustion of the biomass fuel.

The combustion chamber 140 comprises a burner pot 142 and a burner pot holder 144.

The main heating surfaces on the heat exchanger 160 are in the upper portion of the combustion chamber 140. The flames and flue gases from combustion are fired in a vertical direction initially to meet these surfaces. Combustion of the fuel takes place in the burner pot 142 which is made from stainless steel and is of a size, a shape and has strategically located air holes 144 to ensure the correct introduction of primary and secondary combustion air.

The cross sectional profile of the burner pot 142 is of a primary combustion zone 145 with a narrowing 146 of the combustion zone 146 creating a Venturi effect. Primary air holes 147 are located on the base 148 of the pot and a number on the tapered front face 149 and on the sides 150. The size of these holes has been determined to balance the distribution of primary combustion air across the primary combustion zone 145. Initial gasification of the fuel takes place in the primary combustion zone 145. Other orifices in this area include a hole 151 through which heating resistance 152 is located and a hole 153 through which pneumatic air cleaning pipe 154 is located. Extra tolerance is provided in holes 151 and 153 to enable the burner pot 142 to be easily removed for cleaning.

Secondary air holes 155 have been strategically sized and located on the knuckle' 156 in the center of the Venturi narrowing 146 in a secondary combustion zone 157. Air in the secondary combustion zone 157 is evenly distributed to form an air curtain through which the hot gases must pass and the introduction of preheated oxygenated air in this area ensures sufficient secondary combustion of the gases resulting in an afterburner effect.

Tapered side panels 158 are fitted to the top surface of the burner pot 142 to capture a significant amount of debris ejected as a result of the turbulence caused by the increased velocity of the gases through the Venturi. Significant quantities of this debris is further broken down and later ejected as fly ash from the burner. Three notches 159 are positioned on the top surface of the burner pot 142 to ensure correct positioning within the pot holder 144.

The burner pot 142 is located and housed in the holder 144 fitted inside the combustion chamber of the heat exchanger. A function of the holder 144 is to receive combustion air provided by a combustion fan and form a cavity between the outer surfaces of the burner pot 142 and the combustion chamber 140. The burner pot 142 is fitted through an opening in the top surface of the holder 144 and this opening has been formed to ensure correct alignment of the pot within the holder which also ensure correct alignment with the heating resistance 152 and the pneumatic air cleaning pipe 154. Three pins 162, 163, 164 are located to ensure correct positioning of the burner pot 142 in the holder 144. When inserting the pot 142, it is tilted so that the two pins 163, 164 located help reference the corresponding two notches 159 in the burner pot. The front of the pot is then lowered so that pin 162 located in the front notch 159 in the pot. This pivoting effect also aids the location of the heating resistance 152 and pneumatic air cleaning pipe 154 through the rear wall of the pot. The pot is sealed to the top surfaces of the pot holder under the pots own self weight onto a fibre tape seal.

The top internal surfaces 180 of the combustion chamber 140 are designed to receive the hot gases from the burner pot 142 and retain the gases in this area for a period of time.

While in this area, the profile of the combustion chamber roof in area 182 causes the gases to form a vortex and allow all the gases to meet the heat exchange surfaces 180.

The introduction of extra gases from the burner forces these gases in a downwards path to the bottom of free hanging baffle 185. During this downwards travel, some of the gases pass through hotter gases produced by the burner. This leads to further combustion of the residual energy and higher efficiency. The baffle 185 forces the gases against the side wall of the heat exchanger 160 for optimum heat transfer.

The baffle 185 has been designed to allow it to be fitted easily by the user. The baffle 185 hangs under its own self weight against the side of the combustion chamber 140 and is prevented from slipping downwards by two steps 188 which hang on the bottom of opening 190 where the flue gases exit the main combustion chamber 140 and enter heat exchanger tubes 200 which act as a secondary pass. The baffle 185 is prevented from moving horizontally across the combustion chamber by means of a vertical facing flange 202. A nominal tolerance is allowed in the width of the baffle 185 to prevent movement in the front to back plane. The baffle 185 is fabricated in one piece with just a profiling and bending operation. The length of the baffle 185 from top to bottom has been determined to ensure that the bottom of the baffle is low enough to prevent gases exiting the burner 142 from short circuiting the main combustion chamber 140 through the bottom of the baffle and into the secondary pass exchange tubes 200.

Referring to Figures 24 to 28, the secondary pass heat exchanger tubes 200 are maintained free of soot and other deposits by operation of the cleaning crank mechanism 129 and motor 128. The crank mechanism 129 is connected by lifting bars 202 to turbulator 205 which move up and down in the passageway 200 during the closing sequence when the boiler is being turned off. Each turbulator 205 comprises a twisted helix bar 208 to which is attached a square cross section spring 210. The square section profile provides a sharp cutting edge 212 which scrapes against the inner surfaces of the tubes 200.

It is to be understood that the invention is not limited to the specific details described herein which are given by way of example only and that various modifications and alterations are possible without departing from the scope of the invention as defined in the appended claims.

Claims

CLAIMS: 1. An external biomass boiler comprising a slimline housing, one wall of which is adapted to fit adjacent an existing structure, a self-cleaning and automatic ignition wood pellet boiler, an integrated hopper for wood pellets; a burner pot having cleaning means and a secondary pass heat exchanger having separate cleaning means.
2. An external biomass boiler as claimed in Claim 1, further comprising an integrated circulation pump, a water pressure sensor, an air vent and a pressure relief valve.
3. An external biomass boiler as claimed in Claim 1 or Claim 2, in which the burner pot includes a primary combustion zone and a secondary combustion zone, a plurality of air holes in said combustion zones and a narrow knuckle region in the secondary combustion zone adapted to create a Venturi effect and improved secondary combustion.
4. An external biomass boiler as claimed in Claim 3, in which the burner pot holder is provided in the combustion chamber of the boiler and into which the burner pot is removably engageable, the burner pot holder being adapted to receive combustion air provided by a combustion fan and form a cavity between the surfaces of the burner pot and the combustion chamber.
5. An external biomass boiler as claimed in any one of the preceding claims, in which internal surfaces of the upper region of the combustion chamber are adapted to receive the hot gases from the combustion of the fuel and retain the gases for a period of time, the profile of the internal surfaces of the upper region of the combustion chamber forming a vortex allowing the hot gases to contact as much of the heat exchanger surfaces as possible.
6. An external biomass boiler as claimed in any one of the preceding claims including a baffle removably mounted in the combustion chamber, the baffle being adapted to hang in position under its own weight against the side of the combustion chamber and thereby aid the transfer of heat in the heat exchanger of the boiler.
7. An external biomass boiler as claimed in any one of the preceding claims, in which the boiler is provided with one or more secondary pass heat exchanger tubes, cleaning turbulators are provided in the heat exchanger tubes, a cleaning crank mechanism being provided to operate the turbulators, with a square cross-section spring being wrapped about the or each turbulator so as to provide a sharp cleaning edge.
8. An external biomass boiler substantially as herein described with reference to and as shown in the accompanying drawings.