METHOD AND SYSTEM FOR HEATING USING BIOMASS

METHODE ET SYSTEME DE CHAUFFAGE FONDES SUR LA BIOMASSE

English Abstract

A method for producing heat from biomass, comprising: a) combustion and gasification of the biomass; b) combustion of resulting combustion gases in a mixing chamber with controlled admission of ambient air to complete combustion and control temperature of a resulting combustion gas/ambient air mix; c) separation of particulate matters from the resulting combustion gas/ambient air mix; and d) heating air to be heated to a target temperature with a resulting treated air.

French Abstract

Un procédé de production de chaleur à partir de biomasse, comprenant : a) la combustion et la gazéification de la biomasse; b) la combustion des gaz de combustion résultants dans une chambre de mélange avec admission contrôlée de lair ambiant pour achever la combustion et contrôle de la température dun mélange gaz de combustion/air ambiant résultant; c) la séparation des particules du mélange gaz/air ambiant résultant de la combustion; et d) le chauffage de lair à chauffer à une température cible avec lair traité résultant.

Claims

7
WHAT IS CLAIMED IS:
1. A method for producing heat from biomass, comprising:
a) combustion and gasification of the biomass;
b) combustion of resulting combustion gases with a controlled
admission of ambient air, resulting in a combustion gas/ambient air mix;
c) separation of particulate matters from the combustion
gas/ambient air mix, yielding a treated combustion gas; and
d) heating air to be heated to a target temperature with the treated
combustion gas.
2. The method of claim 1, further comprising directing the treated
combustion gas to spaces to be heated.
3. The method of any one of claims 1 and 2, wherein said step b) comprises
controlling a flow of combustion gases and ambient air.
4. The method of any one of claims 1 to 3, wherein said step d) comprises
at least one of:
d1) injecting the treated combustion gas to an air-to-air heat
exchanger; and
d2) passing the treated combustion gas air to a blending chamber.
5. The method of any one of claims 1 to 4, comprising evacuating ashes
produced in step b).
6. The method of anyone of claims 1 to 5, comprising discharging the
particulate matters separated in step c).
7. The method of anyone of claims 1 to 6, wherein said step d) comprises
injecting the treated combustion gas to a hot side of an air-to-air heat
exchanger
and injecting ambient air at a cold side of the heat exchanger.
8. The method of claim 7, comprising controlling a flow of the treated
combustion gas and ambient air within the heat exchanger.

8
9. The method of any one of claims 7 and 8, further comprising directing air
to a waste heat reclaimer downstream of the heat exchanger.
10. The method of any one of claims 7 to 9, comprising controlling the
temperature at the cold side of the air-to-air heat exchanger in step d) and
adjusting
a feed rate of the biomass in step a) and of ambient air in step b) as a
result.
11. The method of anyone of claims 1 to 6, wherein said step d) comprises
using a blending chamber.
12. The method of any one of claims 1 to 11, comprising filtering ambient
air used in steps b) and d).
13. The method of anyone of claims 1 to 12, wherein the biomass is powder
biomass, said step a) comprising using a dust burner.
14. The method of claim 13, said step a) comprising regulating a feed rate
of the biomass powder into the durst burner.
15. The method of any one of claims 13 and 14, wherein said step a)
comprises a multi-staged injection of combustion air into the dust burner.
16. The method of any one of claims 13 to 15, wherein said step a)
comprises controlling a flow of combustion air within the dust burner.
17. The method of any one of claims 1 to 12, wherein the biomass is raw
biomass, said step a) comprising using a furnace.
18. The method of claim 17, said step a) comprising using a refractory-lined
furnace.
19. The method of any one of claims 17 and 18, further comprising
evacuating ashes produced in the furnace.

9
20. A system for producing heat from biomass, comprising:
a combustion/gasification chamber;
a mixing chamber receiving combustion gases from said
combustion/gasification chamber, and controlling mixing of said combustion
gases
with ambient air;
a filtering unit separating particulate matters from a resulting
combustion gas/ambient air mix from said mixing chamber; and
a heat exchanger transferring heat from a resulting filtered air stream
to air to be heated.
21. The system of claim 20, comprising an air blower controlling injection of
ambient air in said mixing chamber.
22. The system of any one of claims 20 and 21, wherein said filtering unit
comprises a multi-cyclone filter.
23. The system of any one of claims 20 to 22, wherein said filtering unit
comprises an ash removal unit.
24. The system of any one of claims 20 to 22, wherein said mixing chamber
comprises an ash removal unit.
25. The system of any one of claims 20 to 24, wherein said heat exchanger
comprises at least one of: an air-to-air heat exchanger and a blending
chamber.
26. The system of any one of claims 20 to 24, wherein said heat exchanger
is an air-to-air heat exchanger, said system comprising a fan injecting the
resulting
filtered air stream to the hot side of said air-to-air heat exchanger and an
air blower
injecting ambient air to the cold side of the heat exchanger.
27. The system of claim 26, comprising at least one temperature sensor
located at an outlet of the cold side of the heat exchanger, and a control
unit
receiving a signal from said sensor, said control unit controlling, from said
signal,
a flow of ambient air into the cold side of the heat exchanger and adjusting a
feed
rate of biomass in said combustion/gasification chamber.

10
28. The system of any one of claims 20 to 27, comprising a ducting unit
delivering a resulting heated air to spaces to be heated.
29. The system of any one of claims 20 to 28, comprising a waste heat
reclaimer.
30. The system of any one of claims 20 to 29, wherein said mixing chamber
comprises controllers of air flow and of temperature within the mixing
chamber.
31. The system of any one of claims 20 to 30, wherein said
combustion/gasification chamber is a dust burner.
32. The system of claim 31, comprising an adjustable biomass feeding unit.
33. The system of any one of claims 20 to 30, wherein said
combustion/gasification chamber is a furnace.
34. The system of claim 33, comprising a dust removal unit for said furnace.
35. The system of any one of claims 20 to 22, wherein said filtering unit
comprises a first ash removal unit and said mixing chamber comprises a second
ash removal unit.

Description

CA 02796040 2012-11-08
TITLE OF THE INVENTION
Method and system for heating using biomass
FIELD OF THE INVENTION
[0001] The present invention relates to heating using biomass. More
specifically, the present invention is concerned with a method and a system
for heating
using biomass.
BACKGROUND OF THE INVENTION
[0002] Large quantities of biomass waste and by-products are created by the
extraction and transformation of wood, such as for example branches or bark,
or from other
sources, such as for example rice husk or animal manure. However, due to its
high
moisture content and other properties, raw, i.e. unconditioned, biomass is
considered
unattractive as a bio-fuel for heating purposes to most potential users in the
industrial
sector. Therefore, raw biomass remains, by and large, unused and underused.
[0003] At the same time, many industries have important heating requirements
owing to the use of large spaces by their labour force for the operation of
their processes;
these heating requirements are mostly satisfied by fossil fuels, such as
natural gas and
heavy oil. Some of these industries, particularly in the field of mining
extraction, are also
located far away from readily accessible sources of fossil-originating energy.
[0004] The cost of fossil fuels is undergoing an upward trend and is slated
to
continue increasing over the long term. In addition, the continued use of
fossil fuels for
heating purposes is a major contributor to the overall emission of green house
gases and its
adverse environmental effects.
[0005] Because of its low cost and its carbon-neutral cycle, raw biomass is
well
positioned to be a fuel of choice for the heating of occupied spaces in an
industrial setting.
However, the large number of technical problems encountered by the use of raw
biomass in
a heating process, as well as the capital, operation and maintenance cost
implied by such a
process render the bio-fuel unpractical in its current form.

CA 02796040 2012-11-08
2
[0006] There is therefore a need in the art for a method and a system for
heating using biomass.
SUMMARY OF THE INVENTION
[0007] More specifically, in accordance with the present invention, there is
provided a method for producing heat from biomass, comprising: a) combustion
and
gasification of the biomass; b) combustion of combustion gases resulting from
said
combustion and gasification of the biomass with a controlled amount of ambient
air; c)
separation of particulate matters from the resulting combustion gas/ambient
air mix; and d)
heating air to be heated to a target temperature with a resulting treated air.
[0008] There is further provided a system for producing heat from biomass,
comprising a combustion/gasification chamber; a mixing chamber receiving
combustion
gases from the combustion/gasification chamber and controlling mixing of the
combustion
gases with ambient air; a filtering unit separating particulate matters from
the resulting
combustion gas/ambient air mix from the mixing chamber; and a heat exchanger
transferring heat from a resulting filtered air stream to air to be heated.
[0009] Other objects, advantages and features of the present invention will
become more apparent upon reading of the following non-restrictive description
of specific
embodiments thereof, given by way of example only with reference to the
accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] In the appended drawings:
[0011] Figure 1 is a diagrammatic representation of a system according to an
embodiment of an aspect of the present invention.
DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0012] The process and system will be described in relation to the
illustrative

CA 02796040 2012-11-08
3
embodiments of Figure 1.
[0013] Either raw or conditioned biomass, or both may thus be used.
[0014] Raw biomass may be first conditioned to a powder having a fine
particle
size, typically less than 1 mm, and low moisture content, typically in a range
between about
2% and 10% on a wet basis. Once thus conditioned, the biomass powder (P) is
fed to a
loading unit 12 in order to fill a storage silo 14, for reserve purposes. The
powder is then
discharged from the silo 14, using a rotating valve 16, onto a dozing conveyor
18 having
variable speed, which transports the powder towards a feeding unit 20 of a
dust burner 22.
A dozing unit, comprising the dozing conveyor 18 and a regulating device 24,
regulates the
feed rate of the biomass powder into the dust burner 22. A multi-staged
injection of
combustion air into the burner 22 is done using primary and secondary air
blowers 26 and
28. Alternatively, the burner 22 may have its own air distribution for the
combustion, thus
requiring only one air fan.
[0015] Alternatively, raw biomass, i.e. under the form of chips rather than
powder, and biomass pellets may be used. In this case, a feeding unit 22a
sends the
biomass to a furnace 22b, as a combustion/gasification chamber in place of the
burner 22,
equipped with combustion fan, igniting unit and control unit. The furnace 22b
may be a
refractory-lined furnace of a moving grate, fixed grate, fluidized bed type
etc. An ash
removal unit 22c allows evacuation of ashes produced in the furnace 22b.
[0016] The hot flue gases produced by the combustion of biomass in the
combustion/gasification chamber, i.e. in the burner 22 in case of powder
biomass or in the
furnace 22b in case of raw biomass or biomass pellets, are ducted to a mixing
chamber 30.
In the mixing chamber 30, the flue gases received from the
combustion/gasification
chamber 22, 22b are mixed with ambient air injected with an ambient air blower
42
equipped with a variable speed motor for example, thereby reducing the
temperature of the
resulting flue gas/ambient air mix, which then allows treatment into a high or
medium
temperature multi-cyclone filter 36. Ashes produced inside the mixing chamber
30 are
evacuated using an ash removal unit 32.

CA 02796040 2012-11-08
4
[0017] The multi-cyclone filter 36 performs the separation of particulate
matters
from the air mix flow, with the particulate matters being discharged using a
rotary airlock
onto an ash removal unit 34.
[0018] Once the flue gas/ambient air mix is thus filtered, an induced draft
(ID)
fan 38 is used to inject the treated air to the hot side of an air-to-air heat
exchanger 40 for
example, and an air blower 42 is used to inject ambient air to the cold side
of the heat
exchanger 40. Once heated, the air stream then continues through a ducting
unit 44 to the
spaces to be heated. Downstream of the heat exchanger 40, air is led to a
waste heat
reclaimer 46, before being sent to a chimney 48 as an exhaust gas.
[0019] A series of variable speed motors, valves and temperature sensors are
used to control the powder's feed rate into the burner 22, as well as the flow
of combustion
air or ambient air into the burner 22, the mixing chamber 30 and the cold side
of the heat
exchanger 40. Namely, temperature sensors located in the mixing chamber 30
transmit a
signal to a Programmable Logic Controller (PLC), to control the air flow into
the mixing
chamber 30 until the desired temperature is reached and maintained.
Furthermore,
temperature sensors located at the outlet of the cold side of the heat
exchanger 40 transmit
a signal to the PLC to control the flow of ambient air into the cold side of
the heat exchanger
40 and to adjust the feed rate of biomass powder and of mixing air, with
interlocks and
timings. The PLC may be used to manage the overall operation of the system,
while a
burner management unit may be responsible for the specific operation of the
burner 22,
when, according to regulations, the burner must have its own management unit
for
example.
[0020] The feed of the burner 22 is modular and adjust to the heat load
requirement. It is equipped with variable speed volume control for the
volumetric feed when
the powder density is relatively consistent. The feeding unit 20 receives
information from
the burner management unit, indicating the required quantity of powder which
must be fed
to the burner 22 in order to respond to the heat load and maintain the flame.
The feed of the
burner may thus handle a wide range of flow rates and respond to a wide range
of heating
requirements.

CA 02796040 2012-11-08
5
[0021] The ambient air may be filtered using air filters 50, before it is
admitted to
the blowers 28 and 42, thereby ensuring that the air delivered to spaces to be
heated is
suitably clean for ventilation and heating occupied spaces.
[0022] Given a desired room temperature of target spaces to be heated, the
invention allows i) feeding the appropriate quantity of powder/combustion air,
ii) treating the
resulting combustion gases, by diluting their temperature in ambient air and
eliminating the
presences of particulates, and iii) using the treated air to transfer heat to
air to be heated.
[0023] In the event that a ratio of ambient air to combustion gases is
sufficiently
high to meet project and environmental requirements, the mixture of ambient
air and
combustion gases are continuously monitored, and the combustion gases are free
of sulfur,
ammoniac or other toxic elements, the system may comprise a blending chamber
instead
of, or in combination with, the air to air heat exchanger 40. As shown in
Figure 1, when the
conditions of the air mixture meet such requirements, a bypass and control
valve 44b may
be used to inject, in part or in total, the air mixture to the ducting unit
44, thereby bypassing
the air to air heat exchanger 40.
[0024] Thus, there is generally provided a air-to-air system and a method
for
production and delivery of heat to spaces in industrial settings, such as
underground
galleries of mines or industrial buildings such as wood transformation plants
for example,
and agricultural buildings, such as green houses or animal raising farms for
example, by
using biomass as a source of fuel.
[0025] The biomass may originate from wood, such as waste or by-product of
the forestry industry, or from other sources, such as agricultural and animal
waste. The
biomass may be conditioned into a dry, fine powder, and the powder's moisture
content and
the particle size controlled to levels suitable for use in a dust burner. Raw
biomass and
biomass pellets may also be used.
[0026] Heat is delivered without injecting flue gases and/or particulate
matter to
the heated spaces, by providing heated ambient air that is free from
combustion products
and, therefore, is suitable for heating areas where human, animal, or plant
activities take
place for example.

CA 02796040 2012-11-08
6
[0027] The method generally comprises feeding biomass to a
combustion/gasification unit and mixing the resulting flue gases with ambient
air in a mixing
chamber to complete the combustion and to reduce the temperature of the flue
gases by
dilution; sensors controlling the temperature of the flue gases/ambient air
mix to the desired
level by admitting ambient air in required amounts, the
combustion/gasification chamber
flame being adjusted by a combined control unit. The resulting flue
gases/ambient air mix is
then stripped of particulate matter. The filtered air is then transported
through a heat
exchanger to heat a cold ambient air stream to a desired room temperature. The
resulting
heated air is then injected in target spaces.
[0028] As people in the art will appreciate, the present method and system
provides heating using biomass, in a manner that does not hinder the air
quality for laborers
or other living matter occupying these spaces.
[0029] The scope of the claims should not be limited by the preferred
embodiments set forth in the examples, but should be given the broadest
interpretation
consistent with the description as a whole.

Representative Drawing