1. Flexigas
Thema D
Dit project is mede mogelijk gemaakt door Samenwerkingsverband Noord Nederland, het ministerie van Economische Zaken, Provincie Groningen en Gemeente Groningen en
wordt ondersteund door Energy Valley
2. - Partners
- Biogas – gas quality
- Temperature measurement
- Ionization measurement
- Future work
3. Partners
- Theme D focuses on the end user: How to combust biogas?
- Hit
• International engineering school, specializing in the field of sensor technology
- Bekaert Combustion Technology
• Manufacturer of burners and aluminum heat exchangers
- Sit
• Develops and manufactures systems designed for the safety, comfort and
performance of gas equipment
- Probably Kiwa Gastechnology
• Provides (inter)national services in the field of gastechnology
• Gas Appliances, Gas Distribution Systems, Gas Quality and Quantity
Measurements en Safety Gas Installations
4. Gas quality
- Gas quality for different countries
- Bandwidth for biogas?
• Dependent on Theme B & C
Source: Afecor conference 2010, Berlin
Based on data from Gasqual and EASEE
gas
Biogas?
5. Air to fuel ratio
- For 1 liter gas, different amounts of air needed to combust
- This changes with changing gas quality
0
5
10
15
20
25
m^3air/m^3gas
Methane
(CH4)
Propane
(C3H8)
H2
G25
(86%CH4,14%N2)
Stoichiometric
Close connected to theme C
6. Air to fuel ratio
- What happens when changing the air to fuel ratio?
- To much air
• Flame lift
- Not enough air
• Hot burner (Flash back)
- Emissions!
• Normal Practice → Lean burn against NOx
So... How much air
do you need?
7. Current System
- Current Boiler systems are set once and have no possibility to
compensate for:
• Gas valve drift
• Temperature change
• Gas quality variation
• Dirt buildup etc
Air
Gas
Gas Valve
Fan
HexVenturi
Negative Pressure
8. Gas adaptive
- Gas adaptive system means: Use a feedback/feed-forward
system for lambda control.
air
gas
control
mixer
sensor
burner hex
general idea of a feed back system
sensor
general idea of a feed forward system
9. Gas adaptive system
- Biogas combustion is a challenge due to variation in gas quality
- Why Gas adaptive systems:
• Modulation With premix burner (1:10 instead of 1:4)
• Optimization of efficiency
• Reduction of combustion products emissions
• Make combustion possible with different gas qualities (Biogas, Russia)
• Ease of Commissioning
• Variation in Altitude
• Lambda control possible extra tool against thermal acoustic instabilities
- Current gas adaptive systems
• More focused on higher modulation range
• Limited focused on gas quality bandwidth (natural gas v.s. biogas)
10. What to measure
- Feedback starts with measurement
• What to measure and which sensors to use?
• Where to measure?
- Different kinds of Measurement possible. Within Flexigas
currently focus on:
• Temperature + air massflow (EBM: Lambda Constant)
• Flame current (SCOT system by Kromschröder / SIT)
12. Temperature measurement
- Lambda Constant (EBM)
• Needs Burner deck temperature and Air mass flow sensing (expensive!)
- Regulate temperature, until correct temperature is reached
Air Mass Flow ->
Temperature->
Excess
air
13. Temperature measurement
- Temperature measurement for lambda-constant system of EBM
- Development to connect thermocouples to burner
• For Furipat ready
• Nit burners:
• Working together with EBM
• Nit is an ‘undefined’ material. How/where to connect thermocouples?
• Working on:
• Reliability testing
• Flash back test
• Temperature Curves
Thermocouples
placed in Furipat
Areas for
thermocouples
(No TC installed)
Nit-material is
knitted steel fibre
15. Ionization measurement
Ionization Pen (80V)
Burner (GND)
Measure Current
(dependent on flame)
80V
Ionization pen already used, but only for flame On/Off
16. Ionization measurement
- Three ‘challenges’ with IO-measurement:
• Not possible yet to get a useful signal at low settings
• For appliances it is the trend to go to 1-2 kW at low power (part of 1:10
modulation)
• ‘Drift’ in the signal. Cause not clear (Ageing of burner?)
• Bekaert and Sit working together on this
• Sagging of the Nit changes the signal
- Fourth: Electrode-burner matching
• Flat characteristic (no massflow meter)
0 500 1000 1500 2000 2500 3000 3500 4000 4500
fan speed [rpm]
ionocurrentG20
CO2 = 9.50 %
CO2 = 8.75 %
CO2 = 8.00 %
Detection
electrode
with shape
matching
burner
17. Ionization measurement
- Sit participates in Flexigas with their ionization measurement
- Their system (GammaSit) is in advanced state
• Uses already present sensors (ionization signal, water temp, fan speed)
• No mass flow meter
• Auto calibrating
- Closed loop control based on ionization current sensor → λ ≈
constant
- How does it cope with biogas?
19. Future work
- Bekaert continues development for the perfect burner for the
needed sensors, while keeping in mind:
• Thermal acoustics
• Lifespan
• Cost
- Hit will investigate alternative ways to measure air to fuel ratio
• Can gas quality be measured when entering the house?
- Bekaert & Sit cooperate with ionization measurement
• Test GammaSit on biogas/low caloric gas
• Thoughts on improving IO-signal
- Sit will continue developing their GammaSit system
- Kiwa Gas Technology wants to participate in Flexigas
• Project proposal: Veiligheid Flexigas (outside Flexigas budget)
• Review current regulations, Which ones are important within Flexigas?
• Alternative measurements for air to fuel ratio
23. - Tendency to higher peak load at low kW
- This means higher modulation
Source: Afecor conference 2010, Berlin
24. - Afecor: is an international association representing the leading
European manufactures of controls for the gas and oil industries
(abbreviation is from French)
26. Principle: chemiluminiscence of combustion
Concentration
dependent signals
Equivalence ratio
CH/OHratio
Two types of turbulent flames
Equivalence ratio
CH/OHratio
Two types of turbulent flames
Predicting equivalence ratio
needs 1 or 2 reference points on
curve:
= UV-photodiode?
Wave length based
(435 nm)
Wave length based
(308 nm)
CH is a radical (short living tracert species) that
exists in the reaction zone of the flame
(flamefront).
OH or hydroxyl radical, is present in the
reaction zone and post flame zone.
The ratio of both radicals is a measure for the
air to fuel ratio or equivalence ratio in the
flame.
The ratio is independent of power and flow
patterns.
Photodiode can be replaced by a photomultiplier or phototransistor.
27. Chemiluminescence measurement
- Development with PMT and photodiodes
- Pro’s
• Very optimistic results with prototype
• Test with feedback on CH4 combustion
• Test with 4 different gasses
• Lambda ‘Controlled’ instead of Lambda ‘Constant’
• Added value for burner or hex ?
- Con’s
• Not evident to extract Lambda information from measured data
• Most development outside the usual burner/Hex development of Bekaert
• Better photodiodes/electronics (Out of reach for Bekaert)
• Software development necessary
• Cooling/anti-fouling development needed necessary
Photodiodes connected
to boiler
28. - For Bekaert chemiluminescence was meant to be developed
under Flexigas
- However, development not pursued and stopped.
30. Ionization measurement and NiT
- Patent request on weld near IO-rod to resist sagging for better IO-
signal in process (large benefit over competition).
• claims
• Prevents the burner deck to change the distance to the ionization rod
• Better ground connection realized, resulting in enhanced ionization signal
• Better heat transport, resulting in reduced aging of the burner deck material
• Better flame stabilization, resulting in a better ionization signal over total power range
- Possible solution for sagging and better control over Io-signal (low
kW settings, flat characteristic)
31. - What happens with more air?
Excess air (λ)
CO NOx
More air
Optimal
point
