UEi EagleX Spécifications télécharger pdf (Page 16)

OMBUST ION

FFICIENC Y

A LCULAT I ONS

This identifies three sources of loss associated with fuel burning:

• Losses due to flue gasses:

- Dry Flue gas loss, Mo i s t u r e and hyd r o g e n ,

- Sensible heat of water va p o r, Unburned gas

• Losses due to re f u s e :

- Combustible in ash, riddlings and dust

• Other losses:

- Radiation, convection, conduction other unmeasured losses

Net efficiency calculations assume that the energy contained in the water vapor (formed as a product of

combustion and from wet fuel) is re c o ve red and the wet loss term is ze r o. Gross efficiency calculations assume that the

energy contained in the water vapor is not re c ove r ed. Since the fuel air mixture is never consistent there is the possibil-

ity of unburned/partially unburned fuel passing through the flue. This is re p r esented by the unburned carbon loss.

Losses due to combustible matter in ashes, riddlings, dust and grit, radiation, convection and conduction are not

i n c l u d e d .

Efficiency Calculation:

• Known Data Fu e l :

- Qgr = Gross Calorific Value (kJ/kg)

- Qnet = Net Calorific Value (kJ/kg)

- K1 = Constant based on Gross or Net Calorific • •

• Known Data Va l u e :

- K1g = ( 255 x %Carbon in fuel )/Qgr

- K1n = ( 255 x %Carbon in fuel )/Qnet

- K2 = % max theoretical CO2 (dry basis)

- K3 = % Wet Loss

- H2 = % Hyd r o g e n

- H2O = % Wa t e r

• Me a s u r ed Da t a :

-Tf = Flue Te m p e r a t u r e

- Ti = Inlet Te m p e r a t u r e

-O2m = % Oxygen in flue gas

-O2r = Oxygen re f e r ence %

• Calculated data:

- Tnet = Net Te m p e r a t u r e

- % CO2 content in flue gas

-% Dry Flue Gas losses

-% Wet losses

-% Unburned carbon loss

-% Ef f i c i e n c y

• Tnet = Flue Te m p e r a t u r e - Inlet Te m p e r a t u r e (or ambient)

• Dry flue gas loss %

= 20.9 x K1 x (Tnet) / K2 x (20.9 - O2m)

• Wet loss %

= 9 x H2 + H2O / Qgr x [2488 + 2.1Tf - 4.2 Ti ]

• Si m p l i f i e d

= [(9 x H2 + H2O) / Qgr] x 2425 x [1 + 0.001 T n e t ]

• Wet loss %

= K3(1+0.001xTnet)

• W h e re K3

= [(9 x H2 + H2O) / Qgr] x 2425

• Net Efficiency %

= 100 - dry flue gas losses

= 100 - 20.9 x K1n x (Tnet) / K2 x (20.9 -O2m)

• Gross Efficiency %

= 100 - {dry flue gas losses + wet losses}

= 100 – {[20.9 x K1g x (Tnet) / K2 x (20.9 - O2m)]+

[K3 x (1 + 0.001 x T n e t t ) ] }

• Excess Air

= [20.9 / (20.9 - O2m) - 1] x 100

• CO2%

= [(20.9 - O2m) x K2 / 20.9]

• Un b u r n e d

= K4 x CO / ( CO + CO2 )

Note: CO scaled in % fuel Loss %

• W h e re K4

= 70 for coke

= 65 for anthracite

= 63 for Bituminous coal

= 62 for coal tar fuel

= 48 for liquid petroleum fuel

= 32 for natural gas

The formula for K4 is based on the gross calorific va l u e

Q g r. To obtain the loss based on net calorific value multi-

ply by Qgr/Qnet. Since this loss is usually small this con-

version has been ignored. This loss is subtracted from the

e f f i c i e n c y.

CO A

REE

C e r tain standards ( ANSI Z21.1) for Carbon Mo n o xide are stated in terms of air-free. Air-free refers to the con-

centration of CO in combustion gases undiluted with flue, or other gases containing little CO. This value is computed

using an equation that takes into account the O2 concentration of the flue gas.

• If 5% O2 is measured (O2m) in the flue then the CO gas value will be recalculated as if 0% we r e measured.

The equation for air-free is as follow s :

- C O af = CO PPM x [(20.9) / (20.9 - O2m)]

• In our example if a reading of 325 PPM we r e measured then the air-free value would be calculated as follows:

- C O af = 325 PPM x [(20.9) / (20.9 - 5)] COaf = 325 PPM x [(20.9) / (15.9)] COaf = 427

We may be given a limit on our gas range by the local authority, which stated that we must not emit more than

400-PPM Carbon Mo n o xide air-free. In the example we would be breaking the limit and corre c t i v e action should be

taken to reduce the level of CO. Air-free values pre vent false readings being submitted, e.g. allowing more air into the

boiler will increase the oxygen level in the flue and dilute any toxic gas reading. Air-free re f e rencing gives readings as if

they we r e undiluted.

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