Two Boilers Hook to Single Turbine

Dry the fuel.

Thank you very much for in suggestion Lyn. The boiler preheat air temperature 220 C. But I can't get the link you send to me.

Thank you very much Lyn. It is possible to remove check valves at both boilers and make them equal pressure. Than each boiler steaming rate dictated by the amount of the fuel being fed. Again this is very unsafe especially one boiler is down for repair and require a good SOP for safe operation. Fortunately both boilers are installed with >60 cu.m per hr feed pumps and can deliver max 85 barg. We are looking at steaming rate of 56 mt @ 12 MW ( 41 mt fully condensing and 15 mt extraction at 12 barg ). Any input for my suggestion. Or any other issues that must be taken care?

How much input has the boiler manufacturer had so far? Telephone calls are immediate, interactive and human.

Potential alterations to the equipment are best addressed using a formal HazOp Study locally.

Are both boiler connected to turbine through a common receiver?

Yes boilers connected to common header and to steam turbine.

Is it a pipe header or a header tank arrangement?

Do not remove the check valves on the steam outlet of the boilers.

Do the two boilers connect to a common header tank before distribution to your turbine(s)?

With single boiler operation the pressure will drop every time cold makeup water is injected. Do you have makeup water (return condensate) preheating?

With two boilers the steam pressure can be stabilised via a large enough header tank. The proviso is that if both boilers are filling up with water and cooling then both boiler pressures will drop. If there are no check valves then the header pressure will drop quickly too.

More info please.

Wal,

Thank you very much!!!

Totally "different" approach-

Modify both boilers- one at a time since you are only running one now- to be high temperature hot water boilers- flooded, making only hot water under pressure so new control will be thermostatic, not pressure.

Operate the boilers at 60 BAR (or JUST below) and make HTHW at 285C (roughly equal to 58.5 BAR, so it will stay as hot water).

Discharge the boilers through a control valve into a flash tank, set to make the 56 BAR steam, with the condensate returning under pressure and being "fed" with make-up water from the dearator. Send the steam to the superheater coils as is done currently.

If the water in the boilers falls slightly below 285C, no problem- it will still flash to make 56 BAR steam.

The boiler and discharge piping should already be rated for 60 BAR, so no added cost there. The make-up water pumps and boiler fill pumps are already rated for 60 BAR equivalent,so no problem there.

The boilers are very likely designed to be able to make HTHW as well as steam, only some of the inlet piping needs to be modified to support water-only operation and you need to install the Low Water cut-off at a different point.

Yes, all of that and answers to the other questions previously lobbed back at the OP would be a bonus.

Sir Thank You Very Much,

Now we are operating one boiler.Feed water temperature 35 C , Deaerator out let 105 C, Detroit water cooled Hydro Grate , Final flue gas design 180 C , But we are getting 230 C because economiser need cleaning , usually the hydro grate increase the temperature by 5 to 7 C . Temperature raise in economizer is 40 to 50 C. Furnace draught still a problem for us because we are getting -7 to -10 mmWC. Design air to fuel is 5 to 1. Secondary and primary air modulated with rpm . FD 35% to 80% and SD 25 to 35%

I don't have full flue gas analysis but the oxygen analyse is brand new and calibrated. We maintain 7 to 10 %. Fuel is palm oil waste or empty bunch fiber. Generally the fuel available from 48 to 55% moisture.

Calorific value around 4500kCal per kg dry. I don't have the unburned ash analysis. But normally 3.5 to 4 % ash to Fuel. Visual judgement the burning is good.

Turbine is extraction ( 13 bar 15mt at 303 C ) the rest goes to condensing. Boiler main 6" and connected to 10" header pipe. To steam turbine 8" . Both boilers and turbine just next to other.

We have a plan to increase the ID fan speed by 7% as per fan manufacture recommendation and the capacity of the electric motor.. It is unfortunate to say that the boiler supplier closed down.

Mr. Dhayanandhan has made the best contribution to this thread.

Only through a complete evaluation of the entire steam and condensate system can a reasonable improvement be made.

I do not believe that a single question has been asked by the OP.

The comments and distinctions between a "steam tank" versus a "steam header" seem silly to me....

It may seem 'silly" but it stops being silly when you have someone down at the receiving end of the steam screaming when the pressure keeps swinging up and down.

To ameliorate The steaming rate swing between boilers...

....you need your boilers feeding into a buffering header tank similar to this...

not a distribution header pipe (aka manifold) like this...

These are shown without lagging.

Your steam plumbing is lagged, yes?

Per Subbharao...

Final flue gas design 180 C , But we are getting 230 C because economiser need cleaning

This should help to start increasing actual output. Clean the economizer and you should gain considerable output to start with.

RG2

There are a couple of points that may assist towards Subbharao's problem :

1. His boilers use Empty Fruit Bunch (55% Moisture) as fuel. Has the boiler firing grate been designed for this ? If so, are you shredding the Empty bunch to sizeable short fibre lengths? This would help in better combustion.

2. Two boilers operating in parallel , supplying steam into a common 10" pipe to operate a 15MW turbine. Lets say that each boiler to take the load of 7.5 MW.But should the Working Pressure between them drop substantially, the boiler with the lower pressure would take 0 MW , while the other with the higher pressure be overloaded to take the full load of 15 MW !This would definitely cause some power outtage and fluctuations. You need to ensure that both boilers are operating with a standard minimum pressure differential - I normally put this at 0.5 barg.

3. Your Feed Water temp at 35 deg c? Isn't that too low? If so, then how does your Deaerator water come up to 105 deg C ?

Just a few pointers, which I hope helps.

Since the boilers are connected in parallel, they will BOTH operate at the same pressure. If the operating pressure of ONE boiler drops significantly, the overall system pressure will drop and the turbine output will fall off substantially.

It is not possible for a boiler to "see" the higher load- the load will fall to the load that can be supported by the reduced pressure.

If just one boiler were connected to the load (not parallel) then the load would be whatever that boiler could support. You cannot fire a boiler at any rate above what the burner is capable of providing.

Fuel in this case is not via a burner, but is solid waste. This means that the boilers are not fired exactly in equal amounts , which is one of the most difficult areas of control. Hence there is ALWAYS a possibility of varying boiler pressures. The steam output have Stop Valves incorporating NR valves, which means that a pressure differential occuring may work against that of the lower pressure. hence the suggestion to have fuel, air and water controls such that this pressure variation does not exceed 0.50 barg.

So the boiler does not have to "see", but the overall system controls how each boiler reacts to the conditions imposed.