3 replies to this topic

[tlp]

Hi all

I need to make a decision on the type of steam boiler to be used in our unit. I've to choose between a Diesel fired boiler and solid fuel boiler.
Steam consumption would be 300kg/hr.

For some practical and investement reasons, we prefer Diesel boiler (Though I know that running cost will be quite high compared to a solid fuel boiler)

I need one critical information regarding Diesel fired boilers. Suppose if the boiler is say designed for 600kg/hr and if the load or utilization is only 300kg/hr, does the fuel consumption reduce by half? or will it be constant depending on the design irrespective of the load or utilazation?

I've one used diesel fired boiler available, but of a higher design or capacity. This information would help me take a decision.

Thanks for the support and advice.

Regards
tlp

[engware]

Hi there:

I would suggest that the oil/diesel type fuel HHV is ~ 18,000 [Btu/lbm] while for coal HHV is ~ 8,000 to 12,000 [Btu/lbm] and wood HHV is ~ 6,000 [Btu/lbm].

Fuel HHV (higher heating value) or the amount of heat released can be used as a value of fuel consumption for a change in load requirements.

Thanks,

Gordan

[kkala]

Steam consumption would be 300kg/hr.
.. Suppose if the boiler is say designed for 600kg/hr and if the load or utilization is only 300kg/hr, does the fuel consumption reduce by half? or will it be constant depending on the design irrespective of the load or utilization?

A lower fuel efficiency is generally expected at load half of the maximum (i.e. fuel consumption somehow higher than the half). This is because boilers are often optimized for about 90% of the maximum possible load for continuous operation.
Nowadays there are boilers with rather flat efficiency curves, even ones optimized for some lower load (I think these are exceptions). Google "boiler efficiency versus load" and look into the results (including article of BBS).
Nevertheless you had better try to get efficiency for several loads from boiler supplier. You consider a Diesel boiler whose size seems small in comparison to typical industrial boilers.

[kkala]

I have looked into the data of one operating boiler, producing 60 ton/h steam (about 40 Barg, 400 oC). At least on paper efficiency changes little with load, being about 92%, 92.5%, 90% at 110%,100%,40% of maximum continuous rating respectively, which means that fuel consumption for 50% load can be approximately considered as half of that for 100% load. In other words increased excess air at lower loads does not seriously affect efficiency.
Of course the size is quite far from a 0.6 ton/h boiler, whose heat losses from surface (radiation+convection) are expected to be a bit higher percentage wise, resulting in a lower efficiency. But efficiency variation with load could be considered insignificant (concerning a modern boiler with controls) for the purposes of (say)a feasibility study.
If you have to chose between boilers (present case), you had better ask for fuel efficiency data from suppliers concerning the specific model of boiler that would be probably selected. Design for 0.6 ton/h boiler may differ from one supplier to the other.
At any case fuel consumption at half load is expected to be a bit higher than half of that for full load, not the same.

Edited by kkala, 05 May 2010 - 02:43 AM.