EP2801540A1

EP2801540A1 - Ventilation system for pellets storage for reduction of carbon monoxide concentrations

Info

Publication number: EP2801540A1
Application number: EP13166613.3A
Authority: EP
Inventors: Randi Mie Jagd Hansen; Jonas Bovin; Kenneth Johst; Gerald Marinitsch
Original assignee: Admede AB
Current assignee: Promedecon GmbH
Priority date: 2013-05-06
Filing date: 2013-05-06
Publication date: 2014-11-12
Anticipated expiration: 2033-05-06
Also published as: EP2801540B1

Abstract

Ventilation system (1) for a biomass pellets storage facility (2), comprising a leak tight pellets feed-in unit (3) between the pellets storage facility (2), a pellets combustion unit (5), and a venting unit (6) connecting the pellets storage facility (2) to the pellets combustion system (5). Within the venting unit (6) ventilation supply air (13) of the pellets storage facility (2) is sucked as combustion supply air (7) into the pellets combustion unit (5). As a result, the air pressure in the venting unit (6) is lower than an air pressure in the pellets storage facility (2), which itself is lower than an atmospheric pressure of the ambient air (10) around the pellets storage facility (2). Carbon monoxide gas (CO) emitted by the pellets inside the pellets storage facility (2) is thereby drawn with the combustion supply air (7) into the pellets combustion system (5). Dangerous carbon monoxide concentrations inside the pellets storage facility (7) are thereby prevented.

Description

The invention concerns a ventilation system for a biomass pellets storage facility, comprising a leak tight pellets feed-in unit between the pellets storage facility and a pellets combustion unit.
Biomass pellets are usually made from dried and milled sawdust and wood shavings that have been compressed into pellets with exemplary dimensions of 10 to 20 mm in length and 3 to 12 mm in diameter. Usually they do not contain any additives or binders. Wood pellet boilers are used in homes and businesses as an alternative to oil or gas fired boilers. They are also being installed to replace coal-fired boilers. In general pellets from biomass create carbon monoxide (CO) while they are stored in storage facilities.
Pellets are usually stored in large sealed containers or in concrete storage rooms that are almost air tight. The pellets storage facility is usually connected via a feeder, for example a screw feeder, to the boiler of a combustion unit. Alternatively, the storage tank can be mounted over the boiler for gravity feeding. Due to the enclosed nature of these storage tanks or rooms, the atmosphere inside can become oxygen depleted and a toxic atmosphere containing carbon monoxide can accumulate. The reason therefore is so far not fully explained, but it is assumed that auto-oxidation processes are responsible for carbon monoxide production from wood pellets.
Even small quantities of wood pellets can produce life-threatening quantities of carbon monoxide in a confined space and that there are various factors that will affect the amount of carbon monoxide produced like storage duration, storage temperature, type of wood used for pellets, available oxygen content, surface area of pellets as well as amount of mechanical abrasion of the pellets during storage.
Consequently the carbon monoxide concentration is increasing over time when the storage facilities are not ventilated properly. Incorporated in this is a risk on human safety in case of the pellets storage facilities have to be inspected. Recently several people were critically injured or died because they entered such storage facilities while the carbon monoxide concentration was above critical levels due to a lack of ventilation.
Carbon monoxide can kill quickly without warning. It is a colourless, odourless and tasteless gas that is highly toxic. When carbon monoxide enters a human body, it prevents the blood from bringing oxygen to cells, tissues and organs.
It follows from the foregoing that it is desirable to have an improved ventilation system for pellets storage facilities that ensures low carbon dioxide concentration within the wood pellet storage facility and avoids safety risks due to carbon dioxide contamination.
Aim of the invention is to provide a ventilation system for pellets storage facilities that overcomes the disadvantages known in the state of the art. This problem is solved for a ventilation system according to the preamble of claim 1 with the features of the characterizing part of claim 1. The subjects of the dependent claims concern further advantageous embodiments of the invention.
A ventilation system for a biomass pellets storage facility according to the invention comprises a leak tight pellets feed-in unit between the pellets storage facility and a pellets combustion unit, wherein at least one venting unit connecting the pellets storage facility to the pellets combustion unit is provided. In this embodiment one or several venting units are realised that connect the pellets storage facility with the pellets combustion unit. Thus a ventilation of the storage facility to reduce the harmful carbon monoxide (CO) content in the facility is provided by the pellets combustion unit. Combustion supply air that is required to operate the pellets combustion unit is supplied via the at least one venting unit from the storage facility. Accordingly carbon monoxide that has formed in the storage facility while storing the biomass pellets like wood pellets or wood chips is transported via the venting unit into the pellets combustion unit and is co-combusted or vented through the burner together with the pellets.
In a further advantageous embodiment of the invention within the at least one venting unit of a ventilation system ventilation supply air of the pellets storage facility is sucked as combustion supply air into the pellets combustion unit. The combustion supply air that is needed to operate the pellets combustion unit is here sucked out of the pellets storage facility. Carbon monoxide that is generated from pellets during storage is sucked as well as the needed combustion supply air into the pellets combustion unit. Advantageously the CO emissions of the pellets storage facility are further oxidized to carbon dioxide in the combustion unit and are sent to a chimney of the combustion unit together with the flue gas of the combustion.
Usefully at a ventilation system according to the invention the pellets storage facility is equipped with at least one direct connection line and/or one indirect connection line to bring in ventilation supply air from an outside to the storage facility. The connection of the pellets storage facility to ambient air in the surroundings outside of a building like a combined biomass heat and power station can be realised either via a direct connection line to bring in ventilation supply air from the outside directly into the storage facility, or via an indirect connection line for instance from the outside to a boiler room or boiler house, respectively, and then further to the pellets storage facility. Within the scope of the invention it is also possible that one or several direct connection lines for ventilation supply air as well as one or several indirect connection lines are combined to safeguard that a sufficient amount of ventilation supply air of ambient air is transported to the pellets storage.
According to another advantageous embodiment of the invention a ventilation system comprises at least one venting unit and/or direct connection line and/or indirect connection line that is/are equipped with a suction device and/or a ventilation device. It might be required and is within the scope of the invention that suction devices like a pump and/or ventilation devices like a fan are installed in the direct and/or indirect connection lines to generate a reduced air pressure within the pellets storage facility compared to the ambient atmospheric pressure. Also the venting unit might be equipped with at least one suction and/or venting device to ensure that carbon monoxide formed within the storage facility is transported together with the combustion supply air into the combustion unit. This at least one suction device and/or ventilation device operates mechanically and is powered electrically, mechanically or pneumatically according to the regulations in force.
Advantageously a ventilation system comprises at least one venting unit that is integrated in the feed-in unit. Thus unintended leakage and back-mixing of carbon monoxide-enriched combustion supply air from the combustion unit to the storage facility is successfully avoided.
Usefully a ventilation system according to the invention comprises several venting units connecting the pellets storage facility and the pellets combustion unit that are arranged at different levels of the pellets storage facility. Advantageously an evenly ventilation of the pellets storage facility is ensured even independent of the level of stored pellets within the storage facility.
In a further development of the invention a ventilation system features a carbon monoxide gas content of the combustion supply air in the venting unit that is higher than a carbon monoxide gas content of the ventilation supply air. The venting unit works like a drain for the carbon monoxide gas content of the pellets storage facility. Thus carbon monoxide that has formed during pellets storage is sucked into the venting unit and further transported to the pellets combustion unit. To be able to determine the gaseous composition of the combustion supply air within the venting unit appropriate gas measurement devices like CO-detectors have to be installed.
A preferred embodiment of the invention comprises a ventilation system in that an air pressure in the pellets storage facility is lower than an atmospheric pressure of the ambient air. Advantageously unintended leakage of ventilation air with an enhanced CO content out of the pellets storage facility is avoided.
Usefully an inventive ventilation system features an air pressure in the venting unit that is lower than an air pressure in the pellets storage facility. With an air pressure difference or pressure gradient, respectively, between the pellets storage facility and the venting unit it is ensured that combustion supply air with an enhanced CO content due to the stored pelletized material is sucked from the storage facility into the combustion unit. Consequently unintended leakage of carbon monoxide out of the pellets storage facility can be avoided.
Advantageously with a ventilation system according to the invention a carbon monoxide content in the pellets storage facility can be kept below a certain limiting value.
Further details and advantages of this ventilation system for pellets storage according to the invention will become more apparent in the following description and the accompanying drawing.
The figure depicts a schematic view of a combined biomass heat and power station with a ventilation system 1 according to the invention. A typical setup of the ventilation system 1 comprises a pellets storage facility 2, a pellets feed-in unit 3 that feeds the pellets from the pellets storage facility 2 in direction 4 to a pellets combustion unit 5, and a venting unit 6 connecting the storage facility 2 to the pellets combustion unit 5. The level of the stored pellets on the lower section of the pellets storage facility 2 is indicated in the figure. Within the venting unit 6 the ventilation supply air is transported in direction 7 from the pellets storage facility 2 as combustion supply air to the pellets combustion unit 5. In a combustion chamber within the pellets combustion unit 5 the wood pellets are combusted together with the combustion supply air and together with the carbon monoxide (CO) formed within the pellets storage facility 2. The off-gas of the combustion unit 5 is then lead as flue gas 8 to a chimney 9 and emitted to the surroundings 10.
The connection of the pellets storage facility 2 to ambient air 10 in the surroundings outside of a combined biomass heat and power station 11 can be realised either via a direct connection line 12 for ventilation supply air 13 from the outside 10 to the storage facility 2, or via an indirect connection line 15 from the outside 10 to a boiler room or boiler house 14, respectively, and further to the pellets storage facility 2. Within the scope of the invention it is also possible that one or several direct connection lines 12 for ventilation supply air 13 as well as one or several indirect connection lines 15 are combined to safeguard a sufficient amount of ventilation supply air 13 of ambient air is transported to the pellets storage 2.
Other alternatives of the connection to ambient air are as well possible but not shown in the figure. For example the venting air of the storage facility 2 could be taken from the boiler room 14 and then be sucked to the boiler 5. In that case the boiler room 14 needs to be vented to the surrounding 10. While the pellets combustion unit 5 is in operation the combustion supply air 7 is sucked out of the pellets storage facility 2. Thus the carbon monoxide formed in the pellets storage facility 2 is exhausted together with combustion supply air in direction 7 into the pellets combustion unit 5. Hereby the carbon monoxide (CO) is oxidised to carbon dioxide (CO₂) within a burner of the combustion unit 5 where the wood chips are combusted due to the high temperature and the presence of oxygen.
Since the combustion air is taken from the pellets storage facility 2 and due to the fact that the storage facility 2 is directly 12 and/or indirectly 15 via the boiler house 14 connected to ambient air 10, the storage facility 2 is sufficiently ventilated and the risk of a high carbon monoxide concentration within the pellets storage facility 2 is significantly reduced. Additionally the environmentally harmful carbon monoxide formed during pellets storage is oxidised to carbon dioxide and emitted only after previous co-combustion in the combustion chamber. This is less harmful to the environment compared with regular ventilation of carbon monoxide laden off-air of the pellets storage facilities as known in the art.
Effective and sufficient ventilation between the pellets storage facility 2 and the pellets combustion unit 5 via the pellets feed-in unit 3 is in most cases not possible since the pellets feed-in unit 3 is usually completely filled with wood chips. The feed-in unit 3 typically comprises a screw conveyor that is also filled quasi gas-tight with pellets that are moved in direction 4 into the combustion unit 5. Accordingly a separate venting unit 6 between the pellets storage facility 2 and the pellets combustion unit 5 is realised, as is depicted in the figure. However, if appropriate structural measures are taken it is also possible to integrate the venting unit 6 in the feed-in unit 3. In such a case an appropriate air supply pipe from the screw conveyor to the roof or ceiling of the storage facility 2 has to be made in order to be able to suck the combustion supply air 7 from the pellets storage facility 2 above the storage level of the pellets.
For example it is within the scope of the invention thinkable to integrate the venting unit 6 within a hollow shaft of a screw feeder that is arranged in the feed-in unit 3. To ensure that no wooden or biomass-containing material will block the venting unit 6 for example a snorkel-like air supply pipe would be required that ends above the storage level of the pellets in the pellets storage facility 2.
Depending on the local regulations of explosion protection measures it may be required to implement several venting units 6 independently of each other between the pellets storage facility 2 and the pellets combustion unit 5 to ensure a fail-safe ventilation system 1. It might also be required and is within the scope of the invention, too, that at least one venting unit 6 includes a suction device 16 like a pump and/or a ventilation device 17 like a fan that generates a reduced pressure within the pellets storage facility 2. Usually such a venting device is implemented as standard equipment in the combustion unit 5. These devices are usually creating a reduced pressure and are sucking the combustion air either from the surroundings or any other connection tube into the combustion system. Thus it is ensured that carbon monoxide formed within the storage facility 2 is transported together with the combustion supply air 7 into the combustion unit 5. This at least one suction device 16 and/or ventilation device 17 operates mechanically and is powered electrically, mechanically or pneumatically according to the regulations in force.

In the figure also the direct air supply connection 12 as well as the indirect air supply connection 15 are equipped with a ventilation device 17 to define the direction of ventilation supply air 13 and avoid leakage of carbon monoxide-enriched ventilation air from the pellets storage facility 2 to the outside 10. The air supply connection 12 might in many cases also be used to refill the storage from time to time with pellets and is therefore not necessarily only a ventilation device.

List of reference signs:

1	ventilation system
2	pellets storage facility
3	pellets feed-in unit
4	direction of pellets feed (arrow)
5	pellets combustion unit
6	venting unit
7	direction of combustion supply air (arrow)
8	direction of flue gas (arrow)
9	chimney
10	outside, ambient air
11	combined biomass heat and power station
12	air supply connection, direct line
13	direction of ventilation supply air (arrow)
14	boiler house
15	air supply connection, indirect line
16	suction device
17	ventilation device

Claims

Ventilation system (1) for a biomass pellets storage facility (2), comprising a leak tight pellets feed-in unit (3) between the pellets storage facility (2) and a pellets combustion unit (5), characterized in that at least one venting unit (6) connecting the pellets storage facility (2) to the pellets combustion system (5) is provided.
Ventilation system (1) according to claim 1, characterized in that within the at least one venting unit (6) ventilation supply air (13) of the pellets storage facility (2) is sucked as combustion supply air (7) into the pellets combustion unit (5).
Ventilation system (1) according to claim 1 or 2, characterised in that the pellets storage facility (2) is equipped with at least one direct connection line (12) and/or one indirect connection line (15) to bring in ventilation supply air (13) from an outside (10) to the storage facility (2).
Ventilation system (1) according to any of the preceding claims, characterized in that at least one venting unit (6) and/or direct connection line (12) and/or indirect connection line (15) is/are equipped with a suction device (16) and/or a ventilation device (17).
Ventilation system (1) according to any of the preceding claims, characterized in that at least one venting unit (6) is integrated in the feed-in unit (3).
Ventilation system (1) according to any of the preceding claims, characterized in that several venting units (6) connecting the pellets storage facility (2) and the pellets combustion unit (5) are arranged at different levels of the pellets storage facility (2).
Ventilation system (1) according to any of the preceding claims, characterized in that a carbon monoxide gas content of the combustion supply air (7) in the venting unit (6) is higher than a carbon monoxide gas content of the ventilation supply air (13).
Ventilation system (1) according to any of the preceding claims, characterized in that an air pressure in the pellets storage facility (2) is lower than an atmospheric pressure of the ambient air (10).
Ventilation system (1) according to any of the preceding claims, characterized in that an air pressure in the venting unit (6) is lower than an air pressure in the pellets storage facility (2).