Power plants – Combustion products used as motive fluid – Process
Reexamination Certificate
2003-03-03
2004-11-23
Gartenberg, Ehud (Department: 3746)
Power plants
Combustion products used as motive fluid
Process
C060S784000, C431S115000
Reexamination Certificate
active
06820432
ABSTRACT:
The present invention relates to methods of operating heat recovery boilers suitable for the combustion of at least one fuel with an incoming stream formed from a stream of hot gases and/or a stream of air, in particular in units for the cogeneration of electricity and heat, typically in the form of steam.
More specifically, the object of the present invention is to provide an improved method, allowing greater flexibility in the use of the boiler and to increase the thermal efficiency thereof, especially in the case of temporary or prolonged decoupling between heat production and electricity production.
To do this, according to one feature of the method according to the invention, between 45 and 80 vol %, advantageously between 50 and 65 vol % and typically between 55 and 65 vol %, of the stream of flue gases produced by the boiler are recycled into the air stream.
According to the invention, substantial recirculation of the flue gases in “air” operating mode makes it possible to utilize the waste heat contained in the flue gases and create a “ballast” of combustion products circulating in the boiler, this ballast increasing the velocity of the flue gases and improving the exchange coefficients, thus making it possible to operate with a low air flow rate, with a very satisfactory thermal efficiency of greater than 90% and possibly exceeding 92%.
In addition, with the method according to the invention the recovery boiler can be used in “fresh air” mode not only temporarily, but continuously, with an optimum efficiency, while maintaining the possibility of subsequently adding an engine or a gas turbine set for driving a generator and delivering the hot gases without requiring to modify the combustion unit of the boiler.
Further features and advantages of the invention will become apparent from the following description of one embodiment, given by way of illustration but implying no limitation, in conjunction with the appended drawing which shows schematically a cogeneration plant for implementing the invention.
The single figures shows a heat recovery boiler
1
, comprising an upstream part incorporating a combustion system
2
(not shown in detail) and a downstream part with a flue
3
for removing the stream of flue gases
4
produced during operation of the boiler. The boiler advantageously includes several exchangers, mainly convective exchangers, forming part of at least one heat-transfer fluid circuit
5
producing, as output, at least one hot working fluid, typically steam.
The combustion system
2
is fed with at least one fuel, typically natural gas or syngas, via at least one line
6
and with an oxidizer gas via a line
7
.
In operation in cogeneration mode, the stream of oxidizer gas sent into the line
7
consists of a stream of exhaust gases from an engine, typically a gas turbine set
8
, driving a generator
9
and having its own fuel feed
10
, typically the fuel also being natural gas or syngas. A set of valves or dampers
11
is used to isolate the inlet line
7
from the outlet of the engine
8
, the exhaust gases from which may be tapped off to a flue, called a bypass
12
.
According one aspect of the invention, running into the line
7
, downstream of the set of valves
11
, are a line
13
, for feeding fresh air slightly compressed by a fan
14
, and a line
15
, for recycling the flue gases escaping from the flue
3
or tapped off upstream of the economizers in the boiler and slightly compressed by a fan
16
. Optionally, the line
15
may run into the line
13
.
REFERENCES:
patent: 4926765 (1990-05-01), Dreizler et al.
patent: 4936088 (1990-06-01), Bell
patent: 5411394 (1995-05-01), Beer et al.
patent: 6095792 (2000-08-01), Berger et al.
patent: 6572674 (2003-06-01), Avart et al.
patent: 1173293 (1964-07-01), None
patent: 0884468 (1998-12-01), None
patent: 1028301 (2000-08-01), None
patent: 9-287418 (1997-11-01), None
French Search Report to FR 02 03068.
Labasque Jacques
Segret Jacques
Gartenberg Ehud
L'Air Liquide, S.A.
Russell Linda K.
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