Oxy boiler power plant with a heat integrated air separation unit

An Air Separation Unit is disclosed which is thermally integrated into a coal fired oxy boiler power plant. The Air Separation Unit has a Dryer with a dryer heater, wherein an extraction line connects the steam extraction port to the dryer heater. A drain line of the dryer heater then fluidly connects the regeneration heater to a point of a Rankine steam cycle fluidly within the condensate system.

TECHNICAL FIELD

The present disclosure relates generally to heat integration schemes applied to coal fired oxy boiler power plant, and more specifically to Air Separation Unit heat integration into such plants.

BACKGROUND INFORMATION

Coal contributes to a large percentage of the electricity generation in the world today and is expected to maintain its dominant share in the foreseeable future. Nonetheless, significant environmental pressures have led to increased environmental demands requiring not only high efficiency but also reduced emission levels of CO2, SO2, NOx, and mercury to ultra-low levels.

A particular advantageous plant arrangement is the use of an Oxy-combustion steam plant with CO2 capture. Oxy-combustion systems use oxygen, usually produced in an air separation unit instead of air, for the combustion of the primary fuel. The oxygen is often mixed with an inert gas, such as recirculated flue gas, in order to keep the combustion temperature at a suitable level. Oxy-combustion processes produce flue gas having CO2, water and O2 as its main constituents, the CO2 concentration being typically greater than about 70% by volume. Therefore, CO2 capture from the flue gas of an oxy-combustion process can be done relatively simply in a Gas Processing Unit.

An example of a typical water steam cycle of a high efficiency oxy-combustion steam plants is shown inFIG. 1. The plant comprises a triple-pressure series of reheat steam turbines HP, IP, LP fed by steam from a boiler142. Exhaust steam from the last low pressure steam turbine LP is condensed in a condenser102before being polished104and pumped via a condenser Extraction pump second stage103successively through a series of low pressure heater106,107,108,109,131, a feed water tank136and high pressure heaters132before returning to the boiler142in a closed loop. The heat source for the low and high pressure heaters is typically steam extracted from the low/intermediate and high pressure steam turbines.

Due to the large benefit in ensuring the highest efficiency cycle there is a continuing need to find ways of better integrating the thermal needs and sinks of the oxy-combustion capture systems within the steam power plant. This requires an optimization of the heat needs and sinks of the capture systems with the plant cycle to ensure no energy is wasted. In particular, these needs take consideration of how to integrate the Air Separation Unit into the condensate cycle.

SUMMARY

A coal fired Oxy boiler with oxygen supply system and flue gas CO2 capture system and a steam cycle power plant scheme is provided that integrates major heat generation sources of the systems in order to provide flexible plant operation and improved overall plant thermal efficiency.

The disclosure attempts to address this problem by means of the subject matters of the independent claim. Advantageous embodiments are given in the dependent claims.

The disclosure is based on the general idea of a novel scheme for thermally incorporating an Air Separation Unit into the condensate system of a coal fired oxy boiler power plant.

An aspect provides a coal fired Oxy boiler power plant comprising a Rankine steam cycle having a high pressure steam turbine, adapted to expand steam, having an exit, an intermediate pressure steam turbine adapted to expand steam from the high pressure steam turbine, and a low pressure steam turbine adapted to expand steam from the intermediate pressure steam turbine having a steam extraction port. A condensate system of the cycle further comprises a condenser adapted to condense steam exhausted from the low pressure steam turbine, a series of low pressure heaters adapted to receive and serially heat condensate from the condenser, a feed water tank configured and arranged to receive condensate from the series of low pressure heaters, and a series of high pressure heaters adapted to receive condensate from the feed water tank.

The oxy boiler power plant further comprises an Air Separation Unit having a Dryer and a dryer regenerator with a dryer heater wherein an extraction line connects the steam extraction port to the dryer heater. A drain line then fluidly connects the regeneration heater to a point of the Rankine steam cycle fluidly between the series of low pressure heater.

In an aspect the intermediate pressure steam turbine is a multi-stage intermediate pressure steam turbine and the steam extraction port is configured and arranged to extract steam from an intermediate stage of the intermediate pressure steam turbine.

In an aspect an emergency line is connected to the drain line and the condenser.

In an aspect a cold reheat line is connected at a first end to the HP steam turbine exit and at a second end to the extraction line.

In a further aspect the cold reheat line includes a control valve.

It is a further object of the invention to overcome or at least ameliorate the disadvantages and shortcomings of the prior art or provide a useful alternative.

Other aspects and advantages of the present disclosure will become apparent from the following description, taken in connection with the accompanying drawings which by way of example illustrate exemplary embodiments of the present invention.

DETAILED DESCRIPTION

Exemplary embodiments of the present disclosure are now described with references to the drawings, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth to provide a thorough understanding of the disclosure. However, the present disclosure may be practiced without these specific details, and is not limited to the exemplary embodiments disclosed herein.

Throughout this specification reference is made to serial units. In this context serial means arranged in a series starting from an upstream end as defined by the nominal flow of working fluid through the unit during it's normal operation.

In an exemplary embodiment shown inFIG. 2, which may be applied to a coal fired oxy boiler power plant shown inFIG. 1, a steam extraction arrangement and condensate return scheme for heat supply to an Air Separation Unit dryer regenerator is provided. As shown inFIG. 2the coal fired oxy boiler power plant comprises a Rankine steam cycle having a high pressure steam turbine HP adapted to expand steam having an exit16, an intermediate pressure steam turbine1having a steam extraction port2adapted to expand steam from the high pressure steam turbine HP, and a low pressure steam turbine LP adapted to expand steam from the intermediate pressure steam turbine1. A condenser15, connected to the low pressure steam turbine LP exhaust, condenses exhausted steam as a first element of a condensate system. From the condenser15, condensate serially passes through a series of low pressure heaters24,25,11,12,20where the condensate is successively heated. From the low pressure heaters24,25,11,12,20condensate flows in a feed water tank which forms the next element of the condensate system. Condensate from the feed water tank23is directed into the last element of the condensate system, a series of High Pressure heaters22.

The oxy boiler power plant further comprises Air Separation Unit having a Dryer with a dryer heater5wherein an extraction line4connects the steam extraction port2to the dryer heater5. A drain line8then fluidly connects the dryer heater5to the condensate system.

In an exemplary embodiment shown inFIG. 2steam is extracted from an IP steam turbine1, preferably from an extraction port2taken from an intermediate stage of a multi stage IP steam turbine, which is typically used as a heat source for at least one of a series of High Pressure Heaters22. In an exemplary embodiment shown inFIG. 2, the extraction system is routed via an extraction line4to a dryer heater5of the Air Separation Unit. The dryer heater5forms part of the Air Separation Unit dryer regeneration system. The steam pressure is controlled, typically to around 19.5 bar by means of an extraction control valve6located in the extraction line4. Depending of the temperature of the extraction steam a de-superheater7may additional be located in the extraction line4upstream of dryer heater5. When the Air Separation Unit dryer is based on molecular sieve technology this enables optimum regeneration temperature by ensuring nitrogen heating temperature of around 200° C. For part load or off-design conditions where pressure of extraction steam is inadequate a cold reheat regeneration steam line18, as shown inFIG. 2, is used. This cold reheat regeneration steam line18connects the HP steam turbine exit16with the extraction line4and is configured with suitable valving to provide an alternate steam source to the IP steam turbine extraction port2. To ensure adequate use of the cold reheat and pressure control to heat exchanger during an operating mode when the cold reheat regeneration steam line18is used to provide steam to the dryer heater5a regeneration steam control valve19may be located in the cold reheat regeneration steam line18.

From the dryer heater5the drain line8directs condensate formed in the dryer heater5to a condensate tank9from where it is pumped by a condensate pump10back into the condensate system. A condensate control valve13located in the drain line8downstream of the condensate pump10provides the condensate tank9with level control. In an exemplary embodiment shown inFIG. 2the condensate is pumped back to the condensate system between the fourth of the series of low pressure heater12and the fifth of the series of low pressure heater20. In an alternative or addition exemplary embodiment shown inFIG. 3, condensate is be pumped back to the condensate system to a point between the fifth of the series of low pressure heaters20and the feed water tank23. In a further exemplary embodiment shown inFIG. 4condensate is be pumped back to the feed water tank23.

In an exemplary embodiment shown inFIG. 2, an emergency line14connects the drain line8to the condenser15. This line is normally closed.

Although the disclosure has been herein shown and described in what is conceived to be the most practical exemplary embodiment, it will be appreciated by those skilled in the art that the present disclosure can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restricted. The scope of the disclosure is indicated by the appended claims rather that the foregoing description and all changes that come within the meaning and range and equivalences thereof are intended to be embraced therein.

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