WO2014138323A1

WO2014138323A1 - Control of mercury emissions

Info

Publication number: WO2014138323A1
Application number: PCT/US2014/020969
Authority: WO
Inventors: James Robert BUTZ; Michael A. Lucarelli
Original assignee: Novinda Corporation
Priority date: 2013-03-06
Filing date: 2014-03-06
Publication date: 2014-09-12

Abstract

Herein is provided a process wherein a mercury sorbent is subjected to an environment wherein thermal degradation and deactivation of the sorbent is expected but wherein the mercury capture is enhanced. In one embodiment, a process includes injecting a phyllosilicate mercury sorbent into the gas outlet between the furnace and the air heater; forming a mercury sorbed phyllosilicate by reacting the phyllosilicate mercury sorbent with mercury carried in the flue gas; and removing the mercury sorbed phyllosilicate from the flue gas with the particulate collection device. In another embodiment, an apparatus includes a particulate injection device adapted to provide a phyllosilicate mercury sorbent to flue gas carried in the gas outlet, the particulate injection device positioned to provide the phyllosilicate mercury sorbent at a location wherein the phyllosilicate mercury sorbent has a residence time in the flue gas of less than 1 second prior to entering the air heater.

Description

CONTROL OF MERCURY EMISSIONS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This disclosure claims the benefit of priority to US Provisional Application

61/773,459 filed 03/06/2013, the disclosure of which is incorporated herein in its entirety.

FIELD OF THE INVENTION

[0002] This disclosure relates to the apparatus and procedure for capturing mercury using a particulate mercury sorbent injected above an air heater in a boiler installation.

BACKGROUND

[0003] Combustion gasses from incinerators, power plants, and coal-fired furnaces typically contain oxides of sulfur (SO_x), oxides of nitrogen (NO_x), and volatile heavy metals such as mercury. On combustion, the mercury is volatilized and carried in the combustion exhaust gasses into the atmosphere.

[0004] Coal-burning electric power plants are the single biggest source of mercury emissions, accounting for 40 percent of the total mercury emitted from all man-made sources. Coal-fired burners account for another 10 percent. Coal fired power stations burning high sulfur bituminous and sub-bituminous coal combustion gases typically discharge combustion gases containing 10-20 μg/Nm³total mercury and 1 to 3 μg/Nm³ elemental mercury (Hg°) from their electrostatic precipitation (ESP) systems. On entering a wet FGD system the ionized and oxidized portion of the total mercury (Hg^x) becomes largely dissolved in the scrubber

SO_x absorption media with approximately 5% of the inbound Hg^x passing through the system. Wet FGD absorption media are typically 25-30% w/w solids dispersions of calcium carbonate, magnesium carbonate, or a mixture thereof and their respective sulphites and sulphates.

[0005] Mercury poses a serious problem for human beings and the environment and as such protection from exposure to mercury pollution has been the subject of US legislation resulting in The Clean Air Mercury Rule of Mar. 15, 2005 and the EPA's Clean Air Interstate Rule (CAIR). Mercury, atomic symbol Hg, is a persistent, bioaccumulative toxic metal that is emitted in combustion gasses in three forms: Elemental mercury, Hg°, oxidized mercury, Hg²⁺ compounds, and particle-bound mercury. After mercury has precipitated from the air and deposited into bodies of water or onto the land, methylmercury is formed by microbial action in the top layers of sediment and soils. Once formed, methylmercury is taken up by aquatic organisms and bioaccumulates up the aquatic food web. Methylmercury is a well-established human neurotoxicant. Methylmercury that is ingested by humans is readily absorbed from the gastrointestinal tract and can cause effects in several organ systems.

[0006] The aim of these regulations is to significantly reduce emissions from coal-fired power plants, the largest remaining sources of mercury emissions in the US. When fully implemented, these rules will reduce utility emissions of mercury from 48 tons a year to 15 tons, a reduction of nearly 70 percent. Typical mercury concentrations in coal are 0.05 to 0.25 mg/Kg. The typical discharge concentrations of total mercury, largely in its elemental form are in the range 2 to 6 μg/Nm³, (where Nm³ is Non-IUPAC nomenclature. N or "normal" refers to gas volumes converted to 0° C and a pressure of 1 .013 bar).

[0007] Efforts to control mercury emissions employ sorbents and/or reactants in attempts to separate the gaseous mercury from the flue gas. Some approaches utilize adsorbents such as powdered activated carbon, silicates, zeolites, clays and ash as solid supports for binding mercury on the surfaces of the solid. Other approaches utilize

sulfide/polysulfide reagents to react with mercury or mercury ions and form mercury sulfides (e.g., cinnabars).

[0008] The utilization of the sorbents/reactants requires providing these materials to the mercury containing flue gas in an active form. Unfortunately, characteristics of the materials like shelf-life and thermal stability deactivate these materials. Numerous techniques have been attempted to overcome the deactivation of the materials; these include on-site preparation, on- site reactivation (see e.g., US Pat. No. 8,069,797) and/or dilution of the active species on a carrier (see e.g., US Pat. No. 7,578,869). Importantly, processes known to deactivate the sorbents/reactants are avoided (e.g., poisoning, fouling, thermal degradation, mechanical damage, and leaching).

SUMMARY

[0009] A first embodiment is a process that includes providing a boiler installation that includes a furnace having a gas outlet which conveys flue gas to an air heater and a particulate collection device; injecting a phyllosilicate mercury sorbent into the gas outlet between the furnace and the air heater; mixing the phyllosilicate mercury sorbent with the flue gas in the gas outlet and in the air heater; forming a mercury sorbed phyllosilicate by reacting the phyllosilicate mercury sorbent with mercury carried in the flue gas; removing the mercury sorbed phyllosilicate from the flue gas with the particulate collection device; and providing a stack emission that includes at least a portion of the flue gas.

[0010] Another embodiment is an apparatus that includes a boiler installation that includes a furnace having a gas outlet that conveys flue gases to an air heater, the air heater upstream of a particulate collection device, and the particulate collection device fluidly connected to a stack; and a first particulate injection device adapted to provide a phyllosilicate mercury sorbent to flue gas carried in the gas outlet, the first particulate injection device further positioned to provide the phyllosilicate mercury sorbent at a location wherein the phyllosilicate mercury sorbent has a residence time in the flue gas of less than 1 second prior to entering the air heater.

BRIEF DESCRIPTION OF THE FIGURES

[0011] For a more complete understanding of the disclosure, reference should be made to the following detailed description and accompanying drawing figures wherein:

[0012] Figure 1 is an illustration of a prior art a coal-fired utility boiler installation of the type used by utilities in the generation of electric power;

[0013] Figure 2 is a plot of data comparing mercury sorbent injection locations and performance;

[0014] Figure 3 is a comparison plot of background/baseline data to the injection of a mercury sorbent above an air heater, as described herein; and

[0015] Figure 4 is the performance over time for the injection of a mercury sorbent above an air heater, as described herein.

[0016] While specific embodiments are illustrated in the figures, with the understanding that the disclosure is intended to be illustrative, these embodiments are not intended to limit the invention described and illustrated herein.

DETAILED DESCRIPTION

[0017] Herein is provided a process wherein a mercury sorbent is subjected to an environment wherein thermal degradation and deactivation of the sorbent is expected but wherein the mercury capture is enhanced. Importantly, the sulfide based mercury sorbents employed herein are known to deactivate (e.g., by sulfide oxidation) at elevated temperatures whereas, the mercury capture by these materials under the herein described process and apparatus provides exceptional mercury capture. [0018] Herein is described a process and apparatus for capturing and removing mercury from the flue gases produced by the combustion of fossil fuels, namely coal. The process involves the hot-side injection of a mercury sorbent, that is the injection of a mercury sorbent between a furnace and an air heater. Preferably, the injection of the mercury sorbent downstream of a SCR unit and upstream of the air heater. Typically, the temperature of the flue gases at the injection point is in excess of 200 °C, 300 °C, or 400 °C. Notably, the temperature of the flue gases at the injection point is less than the temperature in the furnace or at a steam generation unit, for example less than 500 °C.

[0019] Turning briefly to Figure 1 , Figure 1 illustrates a typical boiler installation 10 that includes a furnace 12, air heater 18, particulate collection device 26, wet scrubber 30 and stack 32. In additional detail and proceeding in the direction of flue gas flow generated during the combustion process, the boiler installation 10 includes a furnace 12 having a gas outlet 14 which conveys flue gases, generally designated 16, to an air heater 18 used to preheat incoming air 20 for combustion. Pulverizers 22 grind a fossil fuel 24 (e.g., coal) to a desired fineness and the pulverized coal 24 is conveyed via burners 25 into the furnace 12 where it is burned to release heat used to generate steam for use by a steam turbine-electric generator (not shown). Flue gases 16 produced by the combustion process are conveyed through the gas outlet 14 to the air heater 18 and then to various types of downstream flue gas cleanup equipment. The flue gas cleanup equipment may comprise a particulate collection device (e.g., fabric filter or, as shown, an electrostatic precipitator (ESP)) 26 which removes particulates from the flue gas 16. A flue gas conduit 28 downstream of the particulate collection device 26 conveys the flue gas 16 to a wet scrubber absorber module 30 which is used to remove sulfur dioxide and other contaminants from the flue gas 16. Flue gas 16 exiting from the wet scrubber absorber module or, simply, the wet scrubber 30, is conveyed to a stack 32 and exhausted to atmosphere. Forced draft fans 34 and induced draft fans 36 are used to propel the air 20, fuel 24, and flue gases 16 through the installation 10. For further details of various aspects of such

installations 10 are included in STEAM its generation and use, 40th Ed., Stultz and Kitto, Eds. (1992), Babcock & Wilcox Co., particularly to Chapter 35— Sulfur Dioxide Control, the text of which is hereby incorporated by reference as though fully set forth herein.

[0020] In one embodiment of the process and apparatus for capturing and removing mercury from the flue gases produced by the combustion of fossil fuels described herein is an apparatus that includes a boiler installation 10. The boiler installation 10 includes a furnace 12 having a gas outlet 14 that conveys flue gases 16 to an air heater 18, the air heater 18 upstream of a particulate collection device 26, and the particulate collection device 26 fluidly connected to a stack 32. The apparatus further including a first particulate injection device adapted to provide a phyllosilicate mercury sorbent to flue gas 16 carried in the gas outlet 14. The first particulate injection device further positioned to provide the phyllosilicate mercury sorbent at a location wherein the phyllosilicate mercury sorbent has a residence time in the flue gas of less than two seconds, preferably less than one second, prior to entering the air heater 18. The first particulate injection device includes a first particulate duct injection lance and a means of supplying the phyllosilicate mercury sorbent to the duct injection lance. Preferably, the phyllosilicate mercury sorbent is a powdered material and is supplied to the duct injection lance by the flow of a pressurized gas. Accordingly, the first particulate injection device can further include a means of supplying the pressurized gas (e.g., an air compressor or a pressurized gas tank). The first particulate injection device can include one or more pressurized gas lines in addition to a phyllosilicate mercury sorbent supply line.

[0021] In one example of this embodiment, the apparatus can further include a second particulate injection device. The second particulate injection device can be adapted to provide lime to flue gas 16 carried in the gas outlet 14. The second particulate injection device further positioned to provide the lime at a location wherein the lime has a residence time in the flue gas of less than one second prior to entering the air heater 18. Herein, lime can include calcium oxides and/or calcium hydroxides (e.g., quicklime, slaked lime, or hydrated lime).

[0022] The air heater 18 is typically a heat exchanger. For example, the air heater 18 can be a shell and tube type heat exchanger, a stationary plate heat exchanger, (rotating) regenerative heat exchanger. In one example, the air heater 18 can be adapted to induce turbulent flow on the flue gas. In another example the air heater 18 can be adapted to provide lamellar flow on the flue gas.

[0023] The arrangement of the first and second particulate injection devices can be adjusted to provide for longer residence times prior to the injected particulates entering the air heater 18. In one example, the second particulate injection device is positioned upstream of the first particulate injection device.

[0024] The air heater 18 includes a flue gas inlet and a flue gas outlet. Preferably, the flue gas conduit carrying the flue gas from the flue gas outlet of the air heater 18 includes at least one 90° turn. For example, when an air heater 18 is operated in a position where the flue gas inlet is vertically aligned with the flue gas outlet the flue gas conduit can include a turn sufficient to carry the flue gas in a direction perpendicular to the flow of the flue gas through the air heater 18. Still more preferably, the flue gas conduit makes at least two, even more preferably three, 90° turns prior to depositing the flue gas at a flue gas inlet of the particle collection device.

[0025] The apparatus of the present embodiment can further include a conveyor adapted to carry the phyllosilicate mercury sorbent from a phyllosilicate mercury sorbent reservoir to the first particulate injector. The reservoir can include a silo, preferably with a chute adapted to provide the phyllosilicate mercury sorbent from the silo to a conveying line. The conveying line adapted to provide the phyllosilicate mercury sorbent to duct injection lances. Preferably, the apparatus further includes a blower package adapted to provide a pressurized gas flow through the conveying line and carry the phyllosilicate mercury sorbent to the duct injection lances.

[0026] In another embodiment, the above described apparatus can be used to capture and remove mercury from the flue gases produced by the combustion of fossil fuels. In one example, the process includes providing a boiler installation 10 that includes a furnace 12 having a gas outlet 14 which conveys flue gas 16 to an air heater 18 and a particulate collection device 26; injecting a phyllosilicate mercury sorbent into the gas outlet between the furnace and the air heater 18; mixing the phyllosilicate mercury sorbent with the flue gas in the gas outlet and in the air heater 18; forming a mercury sorbed phyllosilicate by reacting the phyllosilicate mercury sorbent with mercury carried in the flue gas 16; removing the mercury sorbed phyllosilicate from the flue gas 16 with the particulate collection device 26; and providing a stack emission that includes at least a portion of the flue gas 16. The process can additionally include providing less than a two second or less than a one second residence time for the phyllosilicate mercury sorbent in the flue gas prior to the phyllosilicate entering the air heater 18. The phyllosilicate mercury sorbent can be injected into the gas outlet at a location where the flue gas has a temperature in a range of about 200 °C to about 425 °C, about 260 °C to about 370 °C, about 260 °C to about 290 °C, or about 315 °C to about 370 °C.

[0027] Still further, the process can include injecting lime into the gas outlet 14 between the furnace 12 and the air heater 18; and mixing the lime with the flue gas 16 in the gas outlet 14 and in the air heater 18. Herein, lime refers to calcium oxide and/or calcium hydroxide. The lime can be injected into the gas outlet at a location where the flue gas has a temperature in a range of about 200 °C to about 425 °C, about 260 °C to about 370 °C, about 260 °C to about 290 °C, or about 315 °C to about 370 °C. [0028] Preferably, the process results in reducing a mercury concentration in the flue gas by at least 50%, at least 60%, at least 70%, at least 80% across the particulate collection device. That is, the mercury concentration in the flue gas after the particulate collection device is at least 50% less than the mercury concentration in the flue gas after the air heater 18. Still further, the process includes capturing a majority of the mercury in the flue gas at the particulate collection device. The mercury can be sorbed by the particulate mercury sorbent, the fly ash, and/or other particulates in the flue gas or added to the flue gas.

[0029] The process can further include an additional reduction in the mercury concentration in the flue gas before stack emission. Preferably, the mercury concentration is further reduced by about 5% to about 25%, about 5% to about 20%, about 5 to about 15% before the stack emission. This further reduction in mercury concentration can be provided by or achieved using a wet scrubber.

EXAMPLES

[0030] Comparative testing was performed on an apparatus as described above, where the particulate collection device was an ESP (electrostatic precipitator). Flue gas mercury concentrations were determined before the ESP, after the ESP and before the wet scrubber, and after the wet scrubber (corresponding to stack emissions). Injections of the particulate mercury sorbent (e.g., the mercury sorbent provided in the Assignee's US Patents Nos.

6,719,828; 7,048,781 ; and 7,288,499) were performed up-stream of the air heater (as described herein), down-stream of the air heater and up-stream of the particulate collection device, and up-stream of the wet scrubber.

[0031] Figure 2 provides results for the capture of mercury dependent on the location of particulate mercury sorbent injection.

[0032] Figures 3 and 4 provide the results of a 100 hour continuous injection test, where a copper sulfide based phyllosilicate (AMENDED SILICATES available from NOVINDA) is injected up-stream of the air heater at a rate of about 400 Ibs/hr and where hydrated lime is injected up-stream of the air heater at a rate of about 500 Ibs/hr.

Claims

WHAT IS CLAIMED:

1. A process comprising:

providing a boiler installation that includes a furnace having a gas outlet which conveys flue gas to an air heater and a particulate collection device;

injecting a phyllosilicate mercury sorbent into the gas outlet between the furnace and the air heater;

mixing the phyllosilicate mercury sorbent with the flue gas in the gas outlet and in the air heater;

forming a mercury sorbed phyllosilicate by reacting the phyllosilicate mercury sorbent with mercury carried in the flue gas;

removing the mercury sorbed phyllosilicate from the flue gas with the particulate collection device; and

providing a stack emission that includes at least a portion of the flue gas.

2. The process of claim 1 further comprising providing less than a one second residence time for the phyllosilicate mercury sorbent in the flue gas prior to the phyllosilicate entering the air heater.

3. The process of any one of the proceeding claims further comprising injecting lime that comprises a calcium oxide and/or a calcium hydroxide into the gas outlet between the furnace and the air heater; and mixing the lime with the flue gas in the gas outlet and in the air heater.

4. The process of claim 3, wherein the lime is injected into the gas outlet at a location where the flue gas has a temperature in a range of about 200 °C to about 425 °C, about 260 °C to about 370 °C, about 260 °C to about 290 °C, or about 315 °C to about 370 °C.

5. The process of any one of the preceding claims, wherein the phyllosilicate mercury sorbent is injected into the gas outlet at a location where the flue gas has a

temperature in a range of about 200 °C to about 425 °C, about 260 °C to about 370 °C, about 260 °C to about 290 °C, or about 315 °C to about 370 °C.

6. The process of any one of the preceding claims further comprising reducing a mercury concentration in the flue gas by at least 50%, at least 60%, at least 70%, at least 80% across the particulate collection device.

7. The process of claim 6, wherein the mercury concentration is further reduced by about 5% to about 25%, about 5% to about 20%, about 5 to about 15% before the stack emission.

8. The process of claim 7, wherein the mercury concentration is further reduced by a wet scrubber.

9. An apparatus comprising:

a boiler installation that includes a furnace having a gas outlet that conveys flue gases to an air heater, the air heater upstream of a particulate collection device, and the particulate collection device fluidly connected to a stack; and

a first particulate injection device adapted to provide a phyllosilicate mercury sorbent to flue gas carried in the gas outlet, the first particulate injection device further positioned to provide the phyllosilicate mercury sorbent at a location wherein the phyllosilicate mercury sorbent has a residence time in the flue gas of less than 1 second prior to entering the air heater.

10. The apparatus of claim 9 further comprising a second particulate injection device adapted to provide lime to flue gas carried in the gas outlet, the second particulate injection device further positioned to provide the lime at a location wherein the lime has a residence time in the flue gas of less than 1 second prior to entering the air heater.

1 1 . The apparatus of claim 10, wherein the second particulate injection device is positioned upstream of the first particulate injection device.

12. The apparatus of any one of claims 9-1 1 further comprising a conveyor adapted to carry the phyllosilicate mercury sorbent from a phyllosilicate mercury sorbent reservoir to the first particulate injector.