Eclipse Combustion Engineering Guide - Burnerparts
Eclipse Combustion Engineering Guide - Burnerparts
Eclipse Combustion Engineering Guide - Burnerparts
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HEAT BALANCE TABLE<br />
Maximum Load Minimum Load<br />
Heat Balance Conditions Conditions<br />
Component (Full Production Rate) (Empty and Idling)<br />
Heat to load __________Btu/hr ____0____Btu/hr<br />
+ Wall losses + __________Btu/hr + _________Btu/hr<br />
+ Radiation losses + __________Btu/hr + _________Btu/hr<br />
+ Conveyor losses + __________Btu/hr + ____0____Btu/hr<br />
= Available heat = __________Btu/hr = _________Btu/hr<br />
required<br />
÷ Available heat, ÷ __________ ÷ _________<br />
expessed as a<br />
decimal<br />
= Gross heat input = __________Btu/hr = _________Btu/hr<br />
Furnace turndown = Gross heat input, maximum load conditions = _________<br />
Gross heat input, minimum load conditions<br />
Theoretical Thermal efficiency, % =<br />
Heat to load, maximum load conditions<br />
x 100 = _________<br />
Gross heat input, maximum load conditions<br />
Supporting Calculations:<br />
Heat to Load<br />
Heat to load = lb per hour x specific heat x temperature rise.<br />
Specific heats for many materials are listed on pages 37-39.<br />
For most common metals and alloys, use the graphs on page 40.<br />
Simply multiply lb/hr production rate by the heat content<br />
picked from the graph.<br />
Enter the heat to load under Maximum Load Conditions.<br />
Heat to load is usually zero under Minimum Load Conditions<br />
because no material is being processed through the oven or<br />
furnace.<br />
Wall Losses:<br />
Wall loss = Wall Area (inside) x heat loss, Btu/sq ft/hr.<br />
Typical heat loss data are tabulated on page 44 .<br />
If the roof and floor of the furnace are insulated with different<br />
materials than the walls, calculate their losses separately.<br />
Add all the losses together and enter them in both the<br />
Maximum Load and Minimum Load columns above.<br />
Caution: If the furnace is to be idled at a temperature lower<br />
than its normal operating temperature, wall losses will be correspondingly<br />
lower. Calculate them on the basis of the actual<br />
idling temperature.<br />
Radiation Losses:<br />
Radiation Losses = Opening Area x Black Body Radiation<br />
Rate x Shape Factor. See page 49 for radiation rates. Assume<br />
a Shape Factor of 1.<br />
Conveyor Losses:<br />
Treat the conveyor as you would a furnace load.<br />
Conveyor Loss = Lb/hr of conveyor heated x specific heat x<br />
(Temperature leaving furnace – temperature entering furnace)<br />
At minimum load, conveyor losses are usually zero because<br />
no material is being processed through the furnace.<br />
Available Heat:<br />
Available heat = Heat to load + wall losses + radiation losses<br />
+ conveyor losses.<br />
Calculate available heat for both maximum and minimum<br />
load conditions.<br />
Next, consult the available heat charts (page 51) to determine<br />
the percent available heat for the fuel, operating temperature,<br />
and fuel/air ratio conditions of this application.<br />
Enter this figure as a decimal on both sides above.<br />
Gross Input:<br />
Gross Input = Available heat (Btu/hr) ÷ Available heat<br />
(decimal).<br />
Figure this for both maximum and minimum load conditions.<br />
Gross input, maximum conditions, is the maximum heating<br />
input required of the combustion system you select.<br />
Furnace Turndown:<br />
Divide maximum load gross input by minimum load gross<br />
input. The result is the furnace or oven turndown. Your<br />
combustion system must provide at least this much turndown<br />
or the furnace will overshoot setpoint on idle.<br />
Theoretical Thermal Efficiency:<br />
% Efficiency = Heat to load, maximum load conditions x 100<br />
Gross heat input, maximum load conditions<br />
This is the maximum theoretical efficiency of the furnace,<br />
assuming it operates at 100% of rating with no production interruptions<br />
and with a properly adjusted combustion system.<br />
Heat Storage<br />
Heat Storage was left out of this analysis. Althought it is a<br />
factor in furnace efficiency, burner systems are rarely sized<br />
on the heat storage needs of the furnace.<br />
On continuous furnaces where cold startups occur infrequently,<br />
heat storage can usually be ignored without any<br />
major effect on efficiency calculations. On batch-type furnaces<br />
that cycle from hot to cold frequently, storage should be<br />
factored into efficiency calculations.<br />
Heat Storage = Inside refractory surface area, ft 2 x Heat<br />
Storage Capacity, Btu/ft 2<br />
Heat storage capacities for typical types of refractory construction<br />
are tabulated on Page 44.<br />
36