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

- Partners

- Biogas – gas quality

- Temperature measurement

- Ionization measurement

- Future work

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

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

Bio

gas

?

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^3 a

ir / m

^3 g

as

Met

ha

ne

(CH

4)

Pro

pan

e (C

3H

8)

H2

G25

(86%

CH

4, 1

4%N

2)

Stoichiometric

Close connected to theme C

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?

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

FanHexVenturi

Negative Pressure

Gas adaptive

- Gas adaptive system means: Use a feedback/feed-forward system for lambda control.

air

gascontrol

mixer

sensor

burner hex

general idea of a feed back system

sensor

general idea of a feed forward system

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)

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)

Temperature Measurement

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 ->

Tem

per

atur

e -> Excess

air

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

Ionization Measurement

Ionization measurement

Ionization Pen (80V)

Burner (GND)

IonizationProbe

GND, connected to burner

Measure Current (dependent on flame)

80V

Ionization pen already used, but only for flame On/Off

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]

iono c

urrent G

20

CO2 = 9.50 %CO2 = 8.75 %CO2 = 8.00 %

Detection electrode

with shape matching

burner

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?

Future work

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

better together

www.bekaert.com

Extra sheets

Extra slides

- Tendency to higher peak load at low kW

- This means higher modulation

Source: Afecor conference 2010, Berlin

- Afecor: is an international association representing the leading European manufactures of controls for the gas and oil industries (abbreviation is from French)

Chemiluminescence measurement

Principle: chemiluminiscence of combustion

Concentration dependent signals

Equivalence ratio

CH

/OH

rat

io

Two types of turbulent flames

Equivalence ratio

CH

/OH

rat

io

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.

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

- For Bekaert chemiluminescence was meant to be developed under Flexigas

- However, development not pursued and stopped.

Temperature measurement: Setup

- Setup with massflow controllers (100% CH4 used)

Measured Temperature

Signal

Gas or Air

Legend

Air MFC

Gas MFC

Air Compressor

Methane

Gas&Air

Thermocouples

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)

- What happens with more air?

Excess air (λ)

CO NOx

More air

Optimal point