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Destruction of VOC in a Dall Energy Biomass Gasifier at

Warwick Mills

Paper # 17

Presented at the

34th

International Conference on Thermal Treatment Technologies & Hazardous Waste

Combustors

October 20-22, 2015

Houston, TX

Authors:

Jens Dall Bentzen, Managing director Dall Energy,

Venlighedsvej 2, 2970 Hoersholm, Denmark.

E-mail: jdb@dallenergy.com

homepage: www.dallenergy.com

Charlie Howland, Managing director Warwick Mills, at 301 Turnpike Road, PO Box 409, New

Ipswich, NH. www.warwickmills.com

ABSTRACT

Warwick Mills, a factory in New Hampshire, which produces complex fiber composites for the

most challenging safety applications, has installed and commissioned a Dall Energy biomass

gasification plant.

The biomass plant has two main purposes:

- Destroy VOC from coaters in factory

- Produce steam to factory

On September 30 and October 1, 2014, the emissions of the biomass plant were measured.

Test September 30, 2014:

The VOC content in the combustion air was at maximum: 8,000-10,000 ppmv.

The VOC content in the stack was below 1 ppmv. The VOC destruction efficiency was 99.98 %.

Also the particulate content and the NOx in the flue gas were measured:The particulate content

was below 10 mg/Nm3. The NOx was below 60 mg/Nm3 (30 ppmv).

Test October 1, 2014

The VOC content in the combustion air at medium: approximately 3,000 ppmv.

The VOC content in the stack was below 3 ppmv. The VOC destruction efficiency was 99.8 %.

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Also the NOx in the flue gas was measured. The NOx was below 80 mg/Nm3 (40 ppmv).

The VOC content in ambient air, outside the stack, was about 5-10 ppmv, thus higher than inside

the stack.

INTRODUCTION

A new type of biomass and waste combustion system has been developed and implemented in 3

full scale projects: 2 in Denmark and 1 in USA.

The purpose was to develop a combustion system that:

- Can use multiple types of fuels

- Has low emissions

- Can modulate

The purpose of the technology is to produce thermal energy for communities and industries using

low grade solid fuels (MSW, wood wastes). Further,the technology can be used for incineration

of industrial wastes and destruction of VOC.

This paper describe the history of the development of the technology, with focus on the plant at

Warwick Mills in New Hampshire, USA.

The idea behind the development was to take advantage of the benefits within updraft

gasification technology in a combustion system. Updraft gasification is an old, well known

technology which has been used to produce town gas for centuries.

However, updraft gasification has some disadvantages: When the gas is cooled, a large amount

of tars condense, thus plugging up pipes and polluting waste water from the gas condensation

system.

The updraft gasification technology

With updraft gasification, the gasification medium (air/steam) and the produced gas flow

through the gasification reactor in the opposite direction to the fuel bed. The

reactor is fed from above, and the gasification media enters the reactor in the bottom.

With this method of gasification, clearly defined reaction zones arise in the bulk filling. The

sensitive heat of the produced raw gas is used to dry the fuel and to initiate pyrolysis.

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Figure 1. Schematic diagram of an updraft gasifier [2]

As it can be seen in the schematic diagram in Figure 1, the products of decomposition

released in the pyrolysis zone and the steam released as a result of fuel drying

are discharged directly out of the reactor with the producer gas. The tars that are produced in the

pyrolysis zone are not conducted through any hot zone and can therefore not be suitably split up

or oxidized. The tar content in the raw gas can thus reach values over 100 g/Nm3.

The Bioneer updraft gasification system

During the 1980’s the Finnish company Bioneer made 9 commercial district heating systems,

where an updraft gasifier produced gas for use in a gas boiler. The fuels were wood chips and

peat. The plants operated fine, but tars did foul the gas pipe leading from the gasifier into the

boiler. In some plants the gas line was cleaned once every 2-6 weeks (depending on the fuel

properties and output of the gasifier). [1]

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Figure 2. Bioneer-gasifier in the district heating plant of Kauhajoki, Finland [1]

The Babcock&Wilcox Vølund gasification system

During the 1990’s the Danish company Babcock&Wilcox Vølund (BWV) develop a gasification

system for combined heat and power, based on updraft gasification technology.

In the BWV system, the gas is cooled and cleaned and thereafter used in an internal combustion

engine for production of heat and power.

A demonstration plant was built in the Danish town Harboøre, and after a few years the plant

was placed in commercial operation. In the BWV concept, the gas is cooled in a wet cyclone and

wet electrostatic precipitator after the gasifier. There are no problems with fouling of gas pipes,

but the large amounts of tar are dissolved in the scrubber water.

The main technical and financial issue about this technology is the rather complex gas cleaning

and waste water cleaning systems which handle the considerable amounts of tar.

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Figure 3. BWV gasifier (left) and flow diagram at heat and power plant Harboøre (right) [3]

The Dall Energy gasification and gas combustion concept

Previous attempts to make commercial concepts by use of the updraft gasification technology

had problems with the high amounts of tars that are produced in the updraft gasifier.

The idea behind the Dall Energy concept is to burn the tar producing gases produced in the

gasifier above the gasification section in the same reactor as where the gasification takes place.

Hereby, the advantages of the updraft technology will be maintained, while the disadvantage of

tar in the gas will be solved.

Figure 4. Principle diagram of Dall Energy multifuel furnace. [5]

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THE DEVELOPMENT AND IMPLEMENTATION OF THE DALL

TECHNOLOGY

2 MW Pilot plant

In 2009 a 2 MW pilot plant was designed and built in Denmark. The aim of the project was to

verify the objectives of technology: low emissions, stable operation, possibility to run the plant at

low load.

The plan was to find a commercial host for the pilot plant when the objectives had been reached.

Before the plant was built, an extensive study of the gas combustion chamber was made using

CFD modeling to predict low emissions both at low load and full load.

Figure 5. 2 MW Pilot plant (left) and CFD model of CO emission at 20% load [4]

The results of the pilot plant were very successful:

- Dust emission directly out of furnace: 20 mg/Nm3

- CO emission at full load: below detection level

- CO emission at 20% load: below detection level

The plant operator at the local district heating plant in the town Bogense followed the tests of the

pilot plant with great interest which led to negotiations for a full scale demonstrations plant.

8 MW demonstration plant in Denmark The demonstration plant needed to be able to produce 8 MW hot water for district heating. The 2

MW pilot plant could therefore not be used. A new design of an 8 MW furnace was made.

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A contract between Bogense district heating company and the contractor, Weiss A/S, was made

in May 2010. Dall Energy had the task to design the furnace and administrate a grant from the

EUDP program.

The Bogense plant was placed in un-manned, commercial operation in 2012. [6]

Various types of fuels are used in the plant including garden wastes and wood wastes.

Figure 6. 8 MW Demonstration plant in Bogense [4]

Emission tests was made in marts 2012

Table 1. Measurements in flue gas directly out of furnace Parameter Unit Average Average

Load % 100 20

Date dd-mm-yy 20-03-2012 20-03-2012

Measuring period hh:mm 11:12 - 14:22 16:44 - 20:00

Temperature °C 958 845

O2 Vol % (dry) 4.88 5.25

H2O Vol % 38.0 32.4

CO mg/m³(ref) < 2 < 2

NOX mg/m³(s,d) 300 200

NOX mg/m³(ref) 200 140

Particles * mg/m³(s,d) 100 92

Particles * mg/m³(ref) 69 64

Condensable in rinse and condensate mg/m³(s,d) 73 97

Condensable in rinse and condensate mg/m³(ref) 50 68

(s,d) indicates dry gas at standard conditions (0°C, 101,3 kPa) (ref) indicates dry gas at standard conditions (0°C, 101,3 kPa) at 10 % O2

* means "not included in accreditation no. 51"

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2 MW plant for VOC destruction at Warwick Mills

Warwick Mills, New Hamphire, USA is a leader in the engineering of technical textiles for

protective applications. Warwick Mills develops and manufactures complex fiber composites for

the most challenging safety applications.

The advanced manufacturing of safety equipment includes coating of wowen materials with

organic solvents. The ventilation air from the coaters contains Volatile Organic Compounds

(VOC) which needs to be combusted in a thermal oxidizer before the ventilation air can be sent

to the stack.

The fuel bill for the oil based thermal oxidizer was constantly increasing, and the plant manager,

Charlie Howland, started in 2008 to search for biomass technology which could be used instead

of oil. The biomass plant needed to fulfill the strict emission regulations of New Hampshire.

Mr. Howland could not find a biomass technology locally that could fulfill the emission

regulations. In 2010 Mr. Howland made some search via “Google” and found hereby the web

site of Dall Energy, who had published the results of the pilot plant.

Mr. Howland decided to visit Dall Energy in January 2011 to see the pilot plant and the Bogense

plant which at that time was under construction.

Dall Energy and Warwick Mills made thereafter an agreement for the design and build of a

biomass plant for Warwick Mills which would have several purposes:

- Destruction of VOC.

- Production of Steam.

- Control strategy of the plant so destruction of VOC was independent of steam production

- Low load for “stand by” during weekend

- Low particle load in chimney.

During 2011-2012 the building permits were obtained and construction of the plant could start.

The production of the furnace was now ready to start. The size of the plant for Warwick Mills

was the same as the pilot plant built in 2010; and as the pilot plant was no longer in use, Dall

Energy-Warwick agreed that Warwick Mills could buy the pilot plant.

And so the pilot plant was dismantled and shipped from Denmark to USA.

The first start up of the plant was done in April 2014. During the first week of operation, various

points were located to be optimized and adjusted. The plant was shut down and the list of

adjustments was made.

The plant was started up again in June 2014 and has been in operation since then.

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Figure 7 Principle diagram of Dall Energy Furnace at Warwick Mills.

Emission test

The plant is used for destruction of organic solvents in the ventilation air (VOC). It was written

into the permit that an emission test was required at least 6 month after starting the plant. The

emission test must verify that the VOC destruction efficiency was at least 98% and particulates

in the flue gas had to be below 40 mg/Nm3.

The stack test was scheduled for two days: September 30 and October 1 2014.

Test September 30, 2014:

The VOC content in the combustion air was at maximum: 10.000 ppmv.

The VOC content in the stack was below 1 ppmv.

The VOC destruction efficiency was 99.98%.

Also the particulate content and the NOx in the flue gas was measured.

The particle content was below 10 mg/Nm3.

The NOx was below 60 mg/Nm3. (30 ppmv)

Test October 1, 2014

The VOC content in the combustion air was approximately 3000 ppmv.

The VOC content in the stack was below 3 ppmv.

The VOC destruction efficiency was 99.8%.

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Also the NOx in the flue gas was measured.

The NOx was below 80 mg/Nm3. (40 ppmv).

Less emission in stack than in ambient air

Ambient air contained VOC from various sources such as degradation of wood in forest, traffic,

chimneys, etc.

The VOC content in ambient air, outside the stack, was about 5-10 ppmv, thus higher than inside

the stack.

Figure 8 Emission test. Warwick Mills, 2014.

Figure 9 Filters after emission test. Warwick Mills, 2014.

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Operating strategies of the plant

The biomass plant at Warwick Mills has two main purposes:

- Destroy VOC from factory

- Produce steam to the factory

The amount of VOC-loaded air and the need for steam are not related so a new strategy of

operating the plant was developed:

Demand Operating strategies

High Energy demand Increase of primary air until energy demand

fulfilled.

High VOC destruction demand Increase of (VOC loaded) tertiary air

Idle load during weekends

The factory is normally shut down during weekends. An operating strategy for “low chip

consumption” was developed so the plant can keep warm during weekends and only use a very

low amount of wood chips.

On Monday morning the plant can go from “weekend mode” to “full load” in few hours.

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Figure 10 Gasification plant operator, Marcel Alex, (left) and Managing director Charlie

Howland (right) at the Gasifier, June 2015.

A film about the plant can be viewed here: https://www.youtube.com/watch?v=LcBN7xeCOYA

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9 MW plant in Denmark

During 2013-2014, a new 9 MW plant was planned and built in Denmark.

The client is Sønderborg district heating company. The purpose of this plant is to supply cheap

and renewable heat to the Sønderborg district.

The plant was started up in January 2015. Emission tests were carried out in March 2015. The

low emissions of the pilot plant, the Bogense plant and the Warwick plant were verified.

Figure 11 Emissions of NOx, CO and Dust from three Dall Energy plants.

0

100

200

300

400

500

600

700

NOx CO Dust

mg/

Nm

3

Emissions from Dall Energy plants

Danish Limits

Bogense

Sønderborg

Warwick

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Figure 12 9 MW Dall Energy plant in Sønderborg.

RESULTS AND DISCUSSION

A new, multi-fuel, low emission combustion system has been developed.

The technology has been verified in a pilot plant and 3 commercial plants: 2 district heating

plants in Denmark for production of hot water and 1 industrial plant for VOC destruction and

production of steam in USA.

During the projects, the following features have been verified:

- 99.8%-99.98% VOC destruction

- 20-70 mg/Nm3 dust directly out of Furnace

- Fuel flexibility:

- Garden waste, wood waste, wood chips.

- 20-60 % moisture content

- 1-5% ash content

- 10-100 % operating load.

- Stable operation.

ACKNOWLEDGEMENTS

EUDP – The Danish Energy Agency support program who have contributed with financial

support

The Growth fund who have contributed with financial support

The Danish Environmental Agency who have contributed with financial support

The Ministry for Research and Innovation who have contributed with financial support

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REFERENCES

1. OPET Finland, Review of Finnish gasification technologies, OPET Report 4, ESPOO 2002

2. Gasification Guide, Deliverable 8: Biomass gasification – State of the art description.

December 2007.

3. Biomass gasification plants. From web page of Vølund: www.volund.dk

4. Verification and further development of multifuel furnace for biomasse with low NOx and

dust emissions. Danish Energy Agency.

5. Dall Energy homepage www.dallenergy.com

6. Research in Bioenergy, September 2013. http://www.biopress.dk/forside

KEYWORDS

Biomass, multifuel, gasification, VOC, Emissions, NOx, CO, Dust. Environmental