WO2007038605A2 - Flue gas scrubbing with a multifunction impinging stream gas-liquid reactor - Google Patents

Abstract

Certain aspects relating to an impinging stream gas-liquid reactor and to methods of utilizing such reactor in a system for treating flue gas or other gas streams for reduction or removal of pollutants such as sulfur oxides (SOx), nitrogen oxides (NOx), carbon dioxide, particulates, mercury, etc, are described herein. Certain embodiments described herein employ one or multiple groups of horizontal-coaxial impinging stream nozzles, wherein each group includes at least three nozzles.

Description

REMOVAL OF ASH AND SULFUR DIOXIDE IN FLUE GAS WITH A COMBINED MULTIFUNCTION IMPINGING STREAM GAS-LIQUID

REACTOR

RELATED APPLICATIONS This application claims priority under 35 U.S.C. §119 to U.S. Provisional Patent

Application Serial No. 60/721,320, filed September 27, 2005, and entitled "Removal of Ash and Sulfur Dioxide in Flue Gas with a Combined Multifunction Impinging Stream Gas Liquid Reactor", the entire contents of which are hereby incorporated by reference.

BACKGROUND The invention in certain aspects relates to a combined multifunction impinging stream gas-liquid reactor. It is a type of physical-chemical equipment, and may be suitable for performing, for example, gas-liquid reaction(s) or chemical absorption, involving fast reaction(s) in liquid phase, with large gas flow rate, and wet ash removal processes, etc. Gas-liquid reaction or chemical absorption and ash removal from flue gas, are unit operations that have been widely applied in chemical, petroleum, and environmental industries. Depending on the nature of the system involved, especially rate of reaction in liquid phase, slow, medium, or fast, as well as the reversibility, various gas-liquid reaction or chemical absorption processes may be quite different from system to system. Many types of equipment have been used for chemical absorption, including packed column, bubble column, sieve column, injection column, etc.. For systems of fast reaction(s) in liquid phase, spray column and injection scrubber are usually used. However, these systems are typically less efficient, larger in size, and high energy consuming. A major drawback is that the mass transfer coefficients between phases are typically not high, so that overall processes are controlled by mass transfer. Wu et al. patented an impinging stream gas-liquid reactor (Chinese Patent: ZL200420017226.4 incorporated herein by reference; a somewhat similar system and additional subject matter, which constitutes part of the present invention and/or may be useful in the context of the present invention is also described in Example 1, below, and in U.S. Provisional Application No. 60/721,320, filed

September 27, 2005 and entitled, "Removal of Ash and Sulfur Dioxide in Flue Gas with a Combined Multifunction Impinging Stream Gas-Liquid Reactor", by Berzin et al., which is incorporated herein by reference in its entirety), which utilizes impinging streams enhancing mass transfer, and thus the above shortcomings may be mitigated or overcome. However, the above-mentioned gas-liquid reactor of the Chinese patent to Wu et al., due to its structure is limited in the amount of flue gas that can be treated. In addition, the placement of the nozzles can cause, in certain instances part of the pulverized liquid to accumulate on the inner surface of the gas conduits, yielding reduced overall interface for mass transfer and part of the liquid absorbent being wasted. Moreover, measures to reduce undesirable foaming, especially at high gas velocities, produced during operation may be advantageous in certain instances.

Another concern for flue gas treatment is particulates removal. There are many methods currently employed for this purpose, classified into dry and wet processes categories. For dry process, the equipment that can be used include inertia dust remover, cyclone, and electrical ash-remover. The former two can suffer from low efficiency, whereas the later demands more capital investment and high quality installation, with high requirement of maintenance, rendering it economically disadvantageous. For wet processes, there are also many devices currently employed, such as shock washers, venturi dust washers, etc. Typically, wet methods have higher efficiency than dry ones; however, the devices mentioned above also have disadvantages such as larger pressure drops or sometimes low efficiency due to poor contact between gas and liquid.

Utilizing the effect of enhanced inter-phase mass transfer of impinging streams, the current invention aims to mitigate or overcome certain disadvantages of existing devices, providing, in certain embodiments, a technological solution for both gas-liquid reaction(s) and particulate removal, which is simple and compact in structure, multifunctional, able to process large amount of gas flow, and convenient for operation and maintenance with less cost.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying figures, which are schematic and are not intended to be drawn to scale. In the figures, each identical or nearly identical component illustrated is typically represented by a single numeral. For purposes of clarity, not every component is labeled in every figure, nor is every component of each embodiment of the invention shown where illustration is not necessary to allow those of ordinary skill in the art to understand the invention. In the figures:

Fig. 1 shows a cross-sectional view along line 2-2 of a reactor according to one embodiment of the invention; Fig. 2 shows a vertical cross-sectional view of the reactor of Fig. 1 according to one embodiment of the invention;

Fig. 3 shows a top view of the reactor of Fig. 4 according to one embodiment of the invention;

Fig. 4 shows a cross-sectional view of a reactor according to one embodiment of the invention;

Fig. 5 A shows a process flow diagram according to one embodiment of the invention;

Fig. 5B shows a listing of various unit operations and components noted on the process flow diagram of Fig. 5 A according to one embodiment of the invention; Fig. 6 shows a process flow diagram of a gas treatment system according to one embodiment of the invention;

Fig. 7 shows a cross-sectional view of a centrifugal pressure nozzle according to one embodiment of the invention;

Fig. 8 shows a cross-sectional view of a GIS gas-liquid reactor according to one embodiment of the invention;

Fig. 9 shows a process flow diagram of an experimental system according to one embodiment of the invention;

Fig. 10 shows a schematic illustration of a technique for measurement of sizes and size distribution of spray droplets according to one embodiment of the invention; Fig. 11 shows a plot illustrating influence of liquid/gas flow rate ratio on the efficiency of sulfur-remova

MPa) according to one embodiment of the invention;

Fig. 12 shows a plot illustrating influence of Ca/S mole ratio on the efficiency of sulfur-removal

according to one embodiment of the invention;

Fig. 13 shows a plot illustrating sulfur-removal efficiency vs SO₂ concentration in feed g

mol-mol^"1,

MPa) according to one embodiment of the invention;

Fig. 14 shows a plot illustrating influence of concentration of SO₂ in feed gas on gas-film coefficient of mass transfer according to one embodiment of the invention;

Fig. 15 shows a plot illustrating influence of impinging distance on efficiency of sulfur-removal

rn-s^"1,

MPa) according to one embodiment of the invention;

Fig. 16 shows a plot illustrating influence of impinging velocity on

according to one embodiment of the invention;

Fig. 17 shows a plot illustrating influence of impinging velocity on

according to one embodiment of the invention; and

Fig. 18 shows a plot illustrating resistances of the reactor at various impinging velocity according to one embodiment of the invention.

DETAILED DESCRIPTION

The present invention, in certain aspects relates to an impinging stream gas-liquid reactor and to methods of utilizing such reactor in a system for treating flue gas or other gas streams for reduction or removal of pollutants such as sulfur oxides (SOx), nitrogen oxides (NOx); carbon dioxide, particulates, mercury, etc. Certain embodiments of the invention employ one or multiple groups of horizontal-coaxial impinging stream nozzles, wherein each group includes at least three nozzles. In the illustrated embodiment, the reactor 1 includes two groups 8 and 9 of four impinging nozzles. Fig. 1 shows the structure of an exemplary embodiment of the reactor equipment; Fig. 2 shows its vertical cross-sectional view; and Fig. 3 shows a top view of reactor 3 illustrated in Fig. 4.

Referring to Fig. 1, the illustrated reactor comprises a tower body 10 and several groups 8, 9 of impinging stream components, mounted inside the tower body 10 and at various heights. Tower body 10 may be a vertical cylinder. Near the top of the cylinder a mesh can be installed to serve as a foam remover 20. The cylinder has a top cover (which can have an ellipse or conic shape), which is connected to gas discharge port 30. A liquid discharge port 40 is provided at or near the bottom of tower body 10. All groups of impinging stream components, 8, 9, ^•••, may be identical in size and configuration, while Figure 1 shows only groups 8 and 9 as examples, in other embodiments, other groups can be employed. The gas and liquid feed compositions an flow rates may be the same for each group or different. Similarly, for each nozzle of a group, the composition and flow rate may be the same or different from that of other nozzles in the group.

The details of the construction of groups 8 and 9 are described below. For each group, there are at least three, and, as illustrated four gas conduits 50. At the outlet of each gas conduit 50, an atomizing nozzle 60 for liquid (the combination of gas conduit 50 and atomizing nozzle 60 referred to herein as an "ejector"), either essentially purely liquid or optionally containing solid particulates, is installed. Liquid or solid-in-liquid suspension is supplied to nozzles 60 through a high pressure liquid feed pipeline 70. Above the four impinging stream conduits, a foam removal damper 80, which may be elliptical or conical in shape, is placed. Damper 80, tower body 10, and either the bottom portion of tower 10 (i.e. below the top of bracket 8) or damper 80 below the four conduits in upper group 8, can form a sub chamber for flue gas scrubbing. In certain embodiments, for each group, the four gas conduits are divided into two sub-groups, with two conduits in each sub-group. The two conduits in each sub-group may be placed coaxially, such that the outlets of the conduits are facing each other. The conduits may be oriented so that the axes of the two sub-groups of the conduits are essentially perpendicular to each other, and such that the distances from the outlets of the conduits to the center where the two axes meet are equal (See Figure 2), (the distance between the outlets of the two conduits in each sub-group is called "impinging distance"). For each conduit, one nozzle or a set of nozzles can be installed, depending on the requirement of amount of liquid or suspension to be processed. In certain embodiments, the outlet of the nozzle(s) and the outlet of the gas conduit are facing the same direction toward the center of tower body 10.

In certain embodiments, nozzle 60 can comprise a pressure atomization nozzle, or centrifugal pressure nozzle. It certain embodiments, an eddy pressure nozzle (such as that described in Chinese patent no., ZL00230305.1, incorporated herein by reference; see also Example 1, below, and U.S. Provisional Application No. 60/721,320, filed September 27, 2005 and entitled, "Removal of Ash and Sulfur Dioxide in Flue Gas with a Combined Multifunction Impinging Stream Gas-Liquid Reactor", by Berzin et al., which is incorporated herein by reference in its entirety) may be employed. The above- referenced eddy pressure nozzle may be advantageous because it may provide a higher vortex efficiency in certain instances, and thus may require less energy input to sufficiently atomize the liquid or solid-in-liquid suspension.

In the case where solid particulates are present in gas or liquid fed to the reactor, or there is solid product produced from the chemical reaction of the gas and liquid streams, solid particles may have a tendency to clog the mesh of the foam remover 20, resulting in block of the flow channel for gas and increased pressure drop. In such a case, the mesh foam remover may be replaced by an internal wet cyclone 90, as illustrated in Figs. 3 and 4. Figure 4 shows structure of the equipment with the foam remover 20 replaced by an internal wet cyclone 90. Such cyclones are known for other purposes in the art and are commercially available. In certain embodiments, the reactor 1 or 3 is operated continuously. For each group of impinging stream components (e.g. 8, 9. ...etc.), the gas stream GF to be processed may be divided into for equal streams of essentially equal flow rate, supplying each of the four gas conduits 50. The gas stream GF will typically contain at least one component dissolved or suspended therein that is desired to be removed or reduced in concentration in the reactor. Exemplary components may include, for example where GF is a flue gas, SOx, NOx, CO₂, mercury or mercury-containing compounds, particulates, etc. The liquid or solid-in-liquid suspension LF is pressurized and supplied through high pressure liquid feed pipeline 70 to the atomizing nozzles 60, and atomized into tiny droplets in the gas stream to form a droplets-in-gas suspension flow that is injected into the impinging zone IZ - the region of enhancing mass transfer - where the gas-liquid reaction/chemical/physical absorption is carried out. The liquid feed LF may contain dissolved therein one or more reactants selected to be reactive with 'one or more components of stream GF that are desired to be removed or mitigated. For example, for flue gases where removal of SOx is of concern, LF may comprise an aqueous solution of sodium hydroxide and/or calcium hydroxide and/or lime/hydrated lime. Such reagents are effective at converting the SOx to soluble sodium/calcium/magnesium sulfites/sulfates that can be removed from the reactor via liquid outlet 40, thus yielding a gas outlet flow GO reduced in SOx or essentially free of SOx. The above reagents are also effective at removing CO₂ via conversion of the CO₂ into liquid soluble bicarbonates and/or carbonates of calcium/sodium/magnesium. The particular nature and concentrations of the reactants utilized will depend on the particular materials and quantities thereof in the gas feed that are desired to be mitigated as well as the flow rates/throughput desired, and can be selected using routine knowledge of chemistry/chemical engineering principles and routine experimentation and optimization.

When solid particles are present in the GF, liquid droplets atomized by the nozzles will reach their surface in the IZ due to strong mixing and collision effects therein. The surface of the particles are thus wetted and the size and mass of the wetted particle will increase to some extent facilitating their falling by gravity into the bottom of the reactor tower 10. After the reaction/absorption reaction(s) take place, the gas GF flows upwards; while the droplets of liquid or solid-in-liquid suspension may flow in three directions: a small portion of the droplets may descend due to gravity; a portion of the droplets may flow upward driven by the gas flow, where they reach damper(s) 80, are coagulated, and flow downward along the edge of damper(s) 80; and a portion of the droplets may be taken up by the gas flow to the top of the tower 10, where they are separated from the gas stream by the mesh foam remover 20 (Fig. 1) or internal wet cyclone 90 (Fig. 4). If separated by the mesh 20, the liquid will flow downward along the inner wall of the tower 10, while if separated by the wet internal cyclone 90, the liquid/liquid-solid suspension will be discharged to the upper side of the top 85 of foam remover damper 80 (Fig. 4) via outlet 95, and will flow downward along the edge of the damper 80. Those three parts of the liquid or solid-in-liquid suspension will come together at the bottom of the tower 10, and be discharged via the liquid discharge port 40 for disposal or further treatment. In order to isolate the system from the ambient air, in certain embodiments, the discharge port 40 can be connected to a liquid-sealing mechanism. The gas, after having been treated in IZ and flowed through the foam removal damper(s) 80, mesh foam remover 20 or internal wet cyclone 90, will typically be mostly separated from the liquid droplets, and can be released through gas discharge part 30. According to requirement, the gas discharge can be connected for further treatment or vented to atmosphere. In certain embodiments in which it is desired to further remove CO ₂ and/or NOx (e.g. NO₂), the impinging stream reactor may be a component of a photobioreactor-based gas treatment system such as that illustrated in Fig. 6 and described below.

Compared to the typical conventional gas-liquid absorption equipment, the current invention may, in certain embodiments, provide at least one of the following advantages: 1) due to enhancement of mass transfer caused by impinging streams, the limitations of gas side mass transfer to process with fast liquid phase reaction(s) are reduced, resulting in enhanced overall rates of gas-liquid reaction(s)/chemical absorption, and hence enabling a reduction in size of the equipment necessary for large scale process; 2) combined gas-liquid reaction and particle removal processes enables treatment of a wider variety of input streams with pretreatment to remove particulates; 3) using pressure nozzles to atomize the liquid or solid-in-liquid suspension man lead to an increased energy efficiency; 4) installation of the pressure nozzles at the outlet of the gas conduits in certain embodiments, as illustrated in the figures, can reduce or eliminate liquid droplets from reaching the inner wall of the gas feed conduits, which can lead to an undesirable reduction in the liquid-gas surface contact area; 5) use, in certain embodiments, of multiple groups of impinging stream components, with each group including at least three streams (e.g. four streams), may result in an increased capacity for gas flow; 6) employment in certain embodiments of foam removal dampers, together with a mesh foam remover or internal wet cyclone, can allow the system to operated at high gas velocities without foam carry over, thereby reducing the equipment size; 7) use of fewer internal parts than many conventional systems may result in a simpler structure and less capital cost and provide less surface for scaling, thereby reducing maintenance labor and making the reactor more suitable for processes resulting in solid product formation.

Figure 5 A illustrates one embodiment of a gas treatment or pre-treatment system 100 utilizing an impinging stream gas-liquid reactor 101, which can comprise a reactor such as reactor 1 of Fig. 1 or reactor 3 of Fig. 4, of the invention. Gas treatment/pre- treatment system 100 may be utilized to remove, for example, certain pollutants, such as sulfur oxides (SOx, e.g. SO₂) fly ash, etc. from a gas stream, such as flue gas from a power plant, such as a coal-fired power plant. Figure 5B presents a listing of various unit operations and components noted on the process flow diagram of Fig. 5 A and describes such components in greater detail, for a particular exemplary embodiment.

Referring to Fig. 5 A, gas treatment/pre-treatment system 100 comprises an impinging stream gas-liquid reactor 101 to which is fed a gas stream to be treated via line 102, and a liquid stream, containing a reactant composition/absorbent for reacting with/absorbing SOx and/or other components of the gas stream suspended and/or dissolved therein, via line 104. Flue gas from, for example, a gas-fired power plant, etc., is supplied to gas line 102 at inlet 106. In certain embodiments, the composition of the gas can be measured by a gas composition determining device 108. The gas stream is pumped via a blower 110 through a flue gas regulating valve 112 to an optional gas cooling chamber 114, where the temperature of the gas may be reduced via evaporation of a spray of city water through line 116. The chilled and humidified gas stream exits gas cooling chamber 114 and is passed to reactor 101.

Liquid feed introduced to reactor 101 via line 104 can be comprised, at least in part, of a solution or suspension of a chemical absorbent, such as previously described. As illustrated, lime powder is used as the absorbent. Lime powder contained in lime storage/feed tank 118 is introduced to a suspension mixer 120 via a metered conveyor 122. In the suspension mixer 120, the lime powder is mixed with city water supplied via line 124 to the suspension mixer. The suspension/solution produced in suspension mixer 120 is then pumped via pump 126 and line 128 to line 104 and reactor 101. Pressure controller 130 may be included to facilitate, via its control of regulating valve 132, the pressure of the liquid feed supplied to reactor 101 via line 104. Liquid feed that is bled off for pressure control from line 104 prior to introduction into the reactor can be fed back to the suspension mixer 120 via lines 134 and 136.

Gas flow processed by reactor 101, from which one or more undesirable components, such SOx, have been removed, is emitted from reactor 101 via outlet 30 and line 138. Line 138 may include a mass flow meter 140 and a gas composition measuring device 142, if desired. Treated gas in line 138 may, as described previously, either be emitted into the atmosphere or further treated, for example via use of integrated photobioreactor gas treatment system 200 illustrated in Fig. 6, and discussed in more detail below.

Liquid and/or particulates that collect in the bottom of reactor 101 exit the reactor via outlet 40 and line 144 and may be discarded or further processed, for example as described in more detail below and in Fig. 6. In the illustrated embodiment, liquid from reactor 101 is fed to one or more settling pools 146, 146', which can facilitate separation of a liquid fraction from suspended particulates and/or treatment of the liquid or liquid-solid suspension effluent. For example, in certain embodiments, reaction products of the liquid absorbent and gas stream introduced into reactor 101 that become suspended and/or dissolved in the liquid exiting the reactor via line 144 may be settled out and/or precipitated in settling pools 146, 146' to facilitate their removal and disposal or further use or treatment. In certain embodiments, liquid from one or more of the settling pools may be recovered and pumped back to suspension mixer 120 through line 148 via pump 150. Effluent liquid from system 100 exiting the system via either or both of lines 152 and 154 may be, in certain embodiments, disposed of, or further processed or used as, for example, described in more detail below in the context of Fig. 6.

In certain aspects, the invention involves utilization of a gas pre- treatment/treatment system, such gas pre-treatment/treatment system 100 described above in the context of Figs. 5 A and 5B, which is integrated into and forms a part of an overall gas treatment process/system for mitigating pollutants in gases such as flue gas and that incorporates as part of the process/system a photobioreactor apparatus configured to mitigate pollutants such as NOx and/or CO2 and produce biomass that can be utilized as a fuel product or a feed stock for making fuel products or other desirable materials. In certain embodiments, the photobioreactor-based treatment system can utilize algae or other photoautotrophic organisms for converting NOx and/or CO2 into biomass. In certain embodiments, a gas treatment system as described previously, for example gas treatment system 100 of Fig. 5 A, can be utilized as a component of an overall photobioreactor-based gas treatment system, such as those described in commonly owned U.S. Patent Application Publication Number 2005/0064577 Al and International Application Number PCT/US2005/025367, both incorporated herein by reference. For example, in certain embodiments, the invention provides a gas treatment system such as that illustrated in Fig. 7 of Patent Application Publication Number US2005/0064577 Al , in which gas treatment system 100, or components thereof that include impinging stream reactor 101, comprises optional SOx/Hg removal system 942 or 944. In another embodiment, the invention comprises a photobioreactor-based gas treatment system as illustrated in Fig. 9 of International Application Number PCT/US2005/025367, wherein gas treatment system 100, or components thereof that include gas impinging stream reactor 101, comprises optional SOx/Hg removal systems 942 or 944. A schematic flow diagram of a photobioreactor-based flue gas treatment system employing an impinging stream gas liquid reaction system 100, such as illustrated and described above in the context of Fig. 5A, is shown if Fig. 6. Flue gas treatment system 200 can employ a photobioreactor system for mitigation of pollutants, such as NOx and CO2, that may be similar to or essentially identical in configuration to one or more of those described in the above-referenced commonly owned U.S. Patent Application Publication and International Application. Such a photobioreactor system is identified as component 202 in Fig. 6. In the illustrated embodiment, a flue gas producing facility, for example a coal-fired power plant 204, produces a flue gas which is fed to impinging gas-liquid reactor system 100 via line 102. As previously described, one or more pollutants, such as SOx, can be mitigated or essentially removed via reactor system 100 by contacting the flue gas stream with a liquid suspension/solution containing a reactant, such as sodium hydroxide, calcium hydroxide, lime, etc., which stream can be fed to reactor system 100 via line 104. Treated gas, which can be mitigated in at least one component, such as SOx, is emitted from reactor system 100 via line 138 and acts as a feed gas to photobioreactor system 202. Liquid product produced by reactor system 102 exits the system via line 152/154 and may, depending on the particular reactants/absorbents utilized and pollutant components mitigated, contain a solution or a suspension of sodium/calcium sulfite/sulfate or, for operating conditions in which CO2 is absorbed in reactor system 100, sodium/calcium bicarbonate/carbonate. Certain of these products, for example, the sulfite/sulfates, may be further processed, for example via oxidation to produce useful products, for example gypsum. For embodiments wherein liquid stream 152/154 contains bicarbonate/carbonate compounds, the stream may be heated and/or acidified in a heater/mixer 206 to facilitate liberation of CO2 gas, which can be fed to the inlet of photobioreactor system 202 via line 208. As previously described, photobioreactor system 202 can, in certain embodiments, be configured and operated to mitigate certain remaining pollutants in treated gas stream 138, such as NOx and/or CO2 to produce a purified gas stream to 210, which may be released to the atmosphere, and biomass, for example algal biomass 212, which can be utilized as a fuel or processed into a fuel or other useful products.

The following example is intended to illustrate certain embodiments of the present invention, but are not to be construed as limiting and do not exemplify the full scope of the invention.

Example 1

Examples of desulfurization in a sas-continuous impinging streams sas-liquid reactor The nomenclature below is used in the following example. a specific interface area, m^2.m^-3 C concentration, mol/m or kg-m^-3

D_a diameter of absorption chamber, m d_o diameter of gas conduit, m d_p Sauter mean diameter of spray droplets, m

H_a cylinder height of the absorber, m h height of gas conduit axis from lower edge of cylinder, m k film mass transfer coefficient, m^.s^-1

M parameter defined by Eq. (1); also absorption rate of whole the reactor, mol^.s^-1

N mass flux, mol-πf^-s^"1

N' absorption rate per unit volume, mol^.m^-3.-1 Ca/S Ca(OH)₂ to SO₂ mol ratio P pressure, Pa t time, s u_o impinging velocity, i.e., gas velocity at outlet of conduit, m^.s^-1

V volume or volumetric flow rate, m or m -s

Δ increment Subscripts: at atomization

G gas or gas film

L liquid or solid-in-liquid suspension

Lm logarithmic mean R reactor r relative

S SO₂ 7. Introduction

An investigation was made to evaluate the desulfurization of flue gas (DFG) by absorption in a gas-continuous impinging stream gas-liquid reactor for systems involving fast reaction(s) in liquid. The mixture of air and SO₂ was used as the pseudo flue gas and Ca(OH)₂-water suspension as the absorbent. By employing horizontally placed two-impinging streams, the reactor is simple in structure with few internal parts, while it exhibits satisfied overall performance for DFG. Under moderate conditions of liquid-to-gas flow rate rati

nd impinging velocity

m-s^"1, it yields a sulfur-removal efficiency of 92.5%, with the overall pressure drop across the device of 405 Pa only. The influences of some operating and structural parameters, such a

, Ca/S mol ratio, SO₂ concentration in "flue gas", impingement distance S, and nozzle location, etc., were examined. The superficial gas- film mass transfer coefficient, is determined based on mean diameter of spray

droplets. The results show tha

s essentially independent of concentration of SO₂ in flue gas. The relationship between

is fitted to b

ith the standard deviation o

suggesting UQ is a strong effecting variable on mass transfer, and, consequentially, important operational variable. In the range of impinging velocity W₀ from

the values determined for the volumetric mass transfer coefficient, kaa, are d those for are

ranged from 0.00641 to

Air pollution caused by SO₂ in flue gas from coal- and fuel oil-burning is a global issue and thus receives more and more attention. Several schemes, such as fuel pretreatment, concurrent burning and adsorption, and flue gas post treatment (i.e., flue gas desulfurization FGD), have been proposed. Among those schemes, FGD may be the most reasonable one from both technology and economic point of view, making it the most practically applicable. Different categories of processes, such as dry-, semidry-, and wet-processes, have been developed for FGD, while wet-processes exhibit a better promise, due to lower operating cost and more stable operation, and therefore is more widely applied. Since the goal of a wet-process of FGD is primarily for environment protection, the cost and performance are important factors to be considered. Several equipments, e.g., packed column, spray tower, and rotary flowing swirl plate column, etc, were tested, but all those cannot be considered as ideal.

The purpose of the present work is to investigate absorption equipment for industrial application of FGD. Experimental studies were carried out with an impinging stream gas-liquid reactor, wi

n- water suspension as the absorbent, and satisfactory performance was obtained. The internal structure of the device is simple, making it convenient to be operated and maintained. A number of advantages have been exhibited, such as high efficiency and low fluid resistance etc.

2. Selection and design of the reactor 2.1 Adaptability of GIS for FGD

(I)It has been shown that gas-continuous impinging streams (GIS) can enhance transfer between phases very efficiently, providing a solid ground to apply the GIS for FGD.

GIS can be advantageously employed for conditions that involve fast and irreversible reaction(s) in liquid. Such processes are usually controlled by diffusion through gas film, and so can be carried out within very short time under the conditions of strongly enhanced transfer. According to Danckwerts (1970), the feature of a gas- liquid reaction system is characterized by the Parameter M, which is defined as:

The definition of M varies among reaction types, and various expressions of M for different reaction systems can be found in literatures or classical textbooks of chemical reaction engineering. It is indicated that when system is controlled

completely by gas side mass transfer.

In the present example, hydroxide lime suspension was used to absorb sulfur dioxide at low concentration in pseudo flue gas. In the system the following reactions occur in the liquid phase: Dissolution and dissociation of SO₂:

Dissolution and dissociation of the absorbent:

Reaction to yield products of desulfurization:

The system that is under consideration has the followed features: (1) According to

Frank (1991), it can be considered to meet the criteria of

and thus the main reaction in liquid, Eq. 4, is an essentially instant one, and (2) The reaction is essentially irreversible. Hence, it can be expected that the reaction system is where GIS is in the category that GIS is suitable to be applied. 2.2 Other considerations in equipment design

For large scale FGD, low energy cost and maintenance requirement are important. Therefore, the following problems may be considered in reactor design: (1) Atomization of the suspension, and (2) Caking and cleaning.

Berman et al studied SO₂ absorption in coaxial cylinders with impinging streams using pneumatic nozzles were used for atomization. More generally, in typical studies up to date, pneumatic nozzles were used for atomization in GIS. This approach can lead to very high power consumption and complicated equipment.

In the present example, centrifugal pressure nozzles were employed, of which the details will be described in the following section. Such a nozzle can require much less energy to pulverize the liquid suspension, with no requirement for gas compression. Also, the structure of the equipment is relatively simple, with relatively few internal parts, and thus may require less maintenance effort. 2.3 Design of experimental absorption device

2.3.1 Conditions for the system design In order to obtain data of interest for scale up, the experiments were carried out on a small pilot plant scale, and the basic conditions for reactor and system design are listed in Table 1.

2.3.2 Atomizer

The centrifugal pressure nozzles by Wu et al (Chinese Patent: ZL200420017226.4, incorporated herein by reference), were used for atomizing Ca(OH)₂ suspension, and the nozzle structure is briefly shown in Fig. 7. Generally, power consumption for pressure nozzle is only 7-8% of that of a pneumatic one. In the present example, the nozzle

shown in Fig. 7 requires even lower energy than those common ones by 20 to 30%. This is because it employs a highly efficient flow rotating chamber of half empty sphere shape, has compact structure and very short passageway for flows at high pressure. The nozzle head can be made of high-abrasive materials, such as high grade ceramics, to prevent the abrading of the wall by solid particles in the absorbent. 2.2.2 Structure of GIS reactor

A flow configuration of two horizontal coaxial impinging streams is employed in the experimental gas-liquid reactor, and the design is shown in Fig. 8. Two centrifugal pressure nozzles are mounted coaxially and symmetrically inside the two gas conduits. The inlet gas is divided into two streams, together with the spray droplets atomized by the nozzles, flow through the two gas conduits, respectively, at same flow rate. The two mixed streams impinge each other at the center to create the impingement zone with strong turbulence, in which the absorption is carried out. After the short gas-liquid contact, the droplets of absorbent suspension, in which solid Ca(OH)₂ becom

and CaSO₄-2H₂O, drops down by gravity to the bottom of the chamber, and then discharged. A liquid-sealing mechanism is also arranged to prevent shortcut of flue gas to atmosphere. After condensing most of the droplets, gas flows upward and gas liquid is further separated by the damper. The gas is then discharged from the top.

The dimensions of the equipment are: Diameter of absorption chambe

mm, Height of cylinder ves 950 mm, Diameter of gas condui 0 mm, Height

of gas conduit axis from lower edge of the cylinder vessel

mm, and Impinging distance S is adjustable fro

In the present example, the nozzles are placed in two places, as shown in Fig. 8 (Positions A and B). Such arrangement allows to study whether the liquid accelerated by gas flow is beneficial or not. It is also useful to determine the influence of the structure on the performance of the adsorption. If not mentioned, the nozzles are normally placed at Position B.

3 Methods of experiments and data interpretation

3.1 System scheme and experimental procedure Flue gas from coal-burning processes includes N₂, NO_x, CO₂, SO₂, and air. In desulfurization with hydrated lime, N₂ is inert, and the amount of Ca consumed by reaction OfNO_x is negligible; while both CO₂ and SO₂ react with Ca(OH)₂ notably. However, it has been shown that the efficiency of sulfur-removal can be kept constant with the presence of CO₂, provided the molar ratio of Ca/S is above a certain critical value

. This critical values of

r various CO₂ content in flue gas determined by Berman et al (2000) are: 1.6 for

nd 2.0 for CO₂=I 5%. Considering the typical coal burning flue gas consists 500 ppm of SOx and 12% OfCO₂, and 1300 ppm SOx and 8% of CO₂ in fuel oil burning flue gas, the variation o

ay not lead to dramatic increase in bulk Ca(OH)₂ consumption. In addition, temperature of hot flue gas will typically drop down quickly to the wet bulb temperature, close to the room temperature. The concentration change by vaporization of water is insignificant, as the concentration of the suspension is typically low. Thus, it can be assumed that the influence of temperature difference from flue gas on the system is negligible. With these considerations, the present work uses the pseudo flue gas prepared by mixing air and SO₂ at room temperature. The experimental system scheme is shown in Fig. 9. Air and SO₂, in a fixed ratio, are blended in Mixer 306. The resulted pseudo flue gas is divided into two equal mass flow streams to enter Absorber 307. The air flow rate is adjusted by a butterfly valve in the pipeline and measured with a Pitot tube-pressure difference meter, while that of SO₂ by a rotameter. The total gas flow rate is also monitored by a wind velocity meter of DF-3 type at the gas outlet of the reactor. For each run, gas-sampling is performed at both inlet and outlet of the reactor, and the SO₂ concentration in the samples are measured with Iodine-quantitative method to determine the integral amount of SO₂ absorbed in the reactor.

In order to determine the size of the spray droplets in situ, such size was measured by simulating the in situ conditions, using a laser particle measuring instrument of FAM type developed by Shanghai University of Technology. The measurement scheme is illustrated in Fig. 10. To obtain representative samples, the laser beam is arranged to enter and pass through the spray at multipoints, and the data are averaged.

To evaluate the flow resistance of the equipment, the pressure drop Δp, between Point A and B shown in Fig. 9, is measured in each run.

Experimental runs were operated at defined liquid to gas volumetric flow rate ratio, VJVa, while the concentration of Ca(OH)₂ in the absorbent is determined by the requested Ca/S ratio. A diaphragm metric pump was used for liquid transportation through the nozzles to spray. The atomizing pressure has an effect on both amount of liquid sprayed and size of droplets. Since higher pressure will result in more power consumption, while the nozzles used in the present study are of high efficiency, a relative low atomizing pressure o

was selected and for most of the experiments the system was operated at this pressure level. 3.2 Data Interpretation 3.2.1 Assumptions

In addition to sulfur-removal efficiency, mass transfer coefficient is an important parameter of interest. Because of the difficulty in determining the interface area, it is difficult to determine the gas-film transfer coefficient,

, whereas instead, the volumetric ones, kaa, are easier to obtain. The current work aims to obtain th

or, at least a rough estimate.

It is difficult to measure individual parameters locally during operation, therefore the parameters involved are determined by interpreting the global data from the measurements at the inlet and outlet of the device. To do so, the following assumptions are made:

(1) The absorption process is governed by diffusion of SO₂ through gas film, and the equilibrium concentration SO₂ at the interface is equal to 0; (2) The space inside the cylinder and under the damper is the effective region for absorption, in which both gas and sprayed droplets are distributed uniformly and are in ideal mixing. From the existing results, the assumption of ideal mixing is reasonable. However, the droplet distribution is deviated from uniform, and the density in the impingement zone, the active region for gas-liquid contact and mass transfer, is higher. However, since this region has no physical boundary, and the non-uniformity varies from operation to operation, generalization is difficult. On the other hand, values for transfer coefficient based on the whole effective volume

are more meaningful from the point of view of application;

(3) The spray droplets have the same mean residence time in the effective volume as that of gas. The essence of this assumption is that the spray keeps its status and no surface area change during contacting with gas until absorption occurs. For the device shown in Fig. 8, this assumption is reasonable because few internal parts have been employed, and the absorption process can be considered to be carried out before droplets collide on the wall;

(4) The specific surface area for transfer within the effective volume is calculated from the Sauter mean diameter of spray droplets, which keeps constant throughout the process. Because of liquid properties, both re-atomization and coalescence of droplets are possible when the opposed droplets-in-gas suspension streams impinge against each other. The results Wu et al obtained showed the following: large droplets tend to break up (re-atomization) and small ones tend to coalescence so that size distribution becomes narrower, while average diameter of droplets remains essentially unchanged after impingement. This is the experimental evidence for this assumption. 3.2.2 Mass transfer model and its solution

According to Assumption (1), the absorption flux is obtained from the well-known mass transfer model, as

The absorption rate per unit volume is

and that in whole the effective volume of reactor is

According to Assumption (4), the specific interface area calculated from mean diameter of spray droplets, a, is kept constant. Thus, the integral amount of SO₂ absorbed within the residence time of gas in the reactor, At, can be obtained as

Consequentially, the volumetric mass transfer coefficient is obtained from the data measured for the variation in gas composition before and after absorption, CsG₁Im₅ as

where the time interval of gas-liquid contacting, At, is calculated by

and the specific interface area, a, is calculated from the Sauter mean diameter of spray droplets d_p:

In addition, the efficiency of sulfur-removal s defined according to measured

results for gas composition as

4 Results and discussion

4.1 Sizes of spray droplets

As the basis for the determination of mass transfer coefficient, the sizes of droplets of sprayed absorbent suspensions with various concentrations of Ca(OH)₂ atomized at a fixed pressure of 1.0 MPa are measured, and the results are listed in Table 2. As can be seen, the concentration exhibits certain influence on the mean diameter. Since only Sauter mean diameter is used for calculation of specific interface area, the data of size distribution are not given.

4.2 Overall performance of the reactor

As mentioned above, the goal of the present example was to develop a desulfurization equipment of industrial interest. So, understanding its general performance is important. A set of typical operation data measured under stable operation are listed in Table 3. The comparable data are: depending on coal type, SO₂ content in flue gas ranged from 1400 to 11400 mg/m³.

The data listed in Table 3 are representative. The results of the operation are: SO₂ content in the cleaned gas, 240 mg/m³, and the sulfur-removal efficiency is 92.5%, while the pressure drop over the reactor is only 405 Pa. This set of data shows that the designed equipment has satisfied global performance and meets the requisitions for desulfurization by wet process.

4.3 Influence of liquid/ gas ratio on sulfur-removal efficiency For absorption processes controlled by diffusion through gas film, large surface area is favorable. This however, to a large extent, is dependant on liquid-to-gas flow ratio, VJJVG. On the other hand, increase in the ratio leads to increase in power consumption, i.e., increase in cost. Therefore, this ratio is an important parameter to be optimized. The results of this test are shown in Fig. 11. To keep the atomization conditions essentially the same, the experiments are carried out at a fixed liquid flow rate, Vu while gas flow rate, VQ, is controlled according requested

nd Ca(OH)₂ concentration varies to keep Ca/S mol ratio the same at 1.4.

As can be seen from Fig. 11, in the range of

ηs increases continuously as the flow ratio increases. This is likely because the increase in interface area. However, whe

is over 1.0, the change in efficiency ηs is smoothed. Note that increase in

he sam implies gas flow rate and, consequentially, impinging velocity,

decrease. This will lead to smaller transfer coefficient, as shown below. Thus, further increase in this ratio does not improve performance. On the other hand, the removal efficiency tained in the range 0.9 to 1.0 L/m³ fo sufficiently high.

Therefore, this range may be considered to be the optimal. 4.4 Influence of Ca/S molar ratio

The effect of Ca/S molar ratio on s shown in Fig. 12. The experiments are

carried out at a fixed liquid-to-gas ratio, and the requested Ca/S is met by changing concentration of Ca(OH)₂. It can be seen that in the range of

a slightly increasing function of Ca/S, but the variation is small. Note that 77s around 90% implies very low concentration of SO₂ in the cleaned gas ese results testify

that the process indeed is controlled by diffusion through gas film, and fur

in Ca(OH)₂ concentration would not improve performance. In the range of decreases continuously with decreases in Ca/S for the amount of the reagent Ca(OH)₂ is not enough (data not shown). In this range, the reaction between SO₂ and Ca(OH)₂ would proceed quantitatively as described in Section 2.1, without diffusion limitation.

From Fig. 12 it is concluded that, if SO₂ is the only active component, like the pseudo flue gas used in the present study

is the most reasonable ratio. However, in practical flue gas, higher Ca/S may be desireable for CO₂ also consumes some Ca(OH)₂, as mentioned before.

The data shown in Fig. 12 are somewhat different from those by Berman et al, who reported the sulfur-removal efficiency of about 80% under the condition of CO₂=O at CaZS=I.0 (see Fig. 4 in that reference). Likely, this difference resulted from different absorber structures. In that one used by Berman et al, (Berman, Y., Tanldevsky, A., Oren, Y. & Tamir, A. (2000). Modeling and experimental studies of SO₂ absorption in coaxial cylinders with impinging streams— Part i. Chemical Engineering Science, 55: 1009- 1023), spray droplets may collide on the wall rapidly, resulting in a decrease in effective interfacial area.

4.5 Influence of SO 2 concentration in feeding gas

The experimental results on the effect of SO₂ concentration in feeding gas, Cs_G.in, on sulfur-removal efficiency

are shown in Fig. 13. It shows that 77s drops down continuously as

creases. However, this does not imply decrease in absorption rate. In fact, the rate is a simple increasing function o

while the tendency of decrease in 77s resulted from fast increase in the amount of SO₂ needed to be absorbed. These data suggest that, in the case of very high

ertain adjustments of operating conditions, e.g., increasing

etc, is beneficial in order to achieve higher sulfur- removal efficiency.

It is also of interest to understand the effect of SO₂ concentration on gas film transfer coefficient. A set of values for

calculated with the model solution given in Section 3.3.2 from the data yielding Fig. 13 are shown in Fig. 14. The variation of ko is not significant. The maximum relative deviation from the average of the 8 data points,

, is only 25%. If experimental errors and possible deviation from the assumptions are taken into accoun

an be considered to be essentially constant, independent o This suggests that the assumption of gas film diffusion control is

reasonable, and the method for calculating

s also feasible. 4.6 Influences of equipment design

To examine effect of reactor design, the effects of impingement distance and nozzle placement are studied experimentally in a certain range.

The effect of impinging distance, S, is shown in Fig. 15 as a plot of ηs vs the dimensionles

In the range tested, the sulfur-removal efficiency drops down continuously as S becomes smaller. The most likely reason is that increased density of droplets in the impingement zone at smaller S leads to enhanced collision and coalescence between droplets, and thus decreased interface area. On the other hand, the results on fluid resistance of IS contactor by Wu & Wu (1997) showed that once SI do reduced to < 4.0, the pressure drop over IS device increased sharply. So, for both higher absorption efficiency and lower power consumptio

may be a lower boundary for operation. The results on the effect of nozzle placement are listed in Table 4. The values for sulfur-removal efficiency resulting from all the runs with nozzles being placed at Position A are lower than those with nozzles at Position B. For the tests with nozzles at position A, it was found that the cross sectional area of the gas conduit designed according to reasonable velocity does not match that of sprays from the nozzles: the former is smaller than the latter. As a result, part of droplets are sprayed onto the inside wall of the conduits directly, and assemble together to form liquid film. The latter moves out along conduit wall, and finally drop down to the bottom of the reactor. Due to its very small surface area, basically this part of liquid is not active. On the other hand, it is also observed that, the spray droplets from pressure nozzle have considerably high axial velocity, and no acceleration by gas stream appears to be needed. Thus, Position B (represented by the dashed lines in Fig. 8) gives better performance for adsorption.

4.7 Interpretation of mass transfer coefficient Traditionally, interpretation of data on mass transfer coefficient is based on the π- law, in which certain dimensionless numbers are used. However, phenomena included in IS are much more complex due to the impingement between the opposed streams. In fact, Wu et al (Wu, Yuan, Xiao, Yang & Zhou, Yuxin (2003). Micromixing in the submerged circulative impinging stream reactor. Chinese J. ofChem. Eng., 11(4): 420- 425) have found in a study on micromixing that Reynolds number, Re, cannot be used as a criterion in scaling-up. In addition, mass transfer coefficient generally depends on the relative velocity between phases, U_x. In IS operation, however, the movement of droplets is very complex. They may penetrate to and fro between opposed streams and thus experience accelerating and decelerating moving stages. As a result, u_τ varies from time to time and the variation regularity varies from operation to operation, makes it difficult to determine any representative time-averaged value of

In the present study, gas-film mass transfer coefficient,

is interrelated to the impinging velocity,

i-e., the velocity of gas flow at the outlet of the conduit. The values for

calculated by the equations given in Section 3.2.2 from the data yielding Fig. 12 are shown in Fig. 16. By regression, the data are fitted to give:

with the standard deviation o

The power of 1.75821 suggests that W₀ has an effect on ICQ, and thus is an important operating condition.

The volumetric mass transfer coefficient,

is also calculated from the same set of data as for &_G, and the results are given in Fig. 17. The relationship between k^a and M₀ is nearly linear, quite different from that betwee

should be noted that this set of experiments is carried out at a constant liquid flow rate,

On one hand, higher uo implies larger gas flow rate, VQ, resulting in shorter residence time, i.e., smaller absorbent mass per unit effective volume of the reactor. On the other hand, with constant Ca/S ratio, larger VQ correlates with a need for higher concentration of Ca(OH)₂ in absorbent, yielding larger Sauter mean diameter of spray droplets (see Table 2) and thus smaller interface area per unit mass of absorbent. So, increase in M₀ has a double negative effect on the specific surface area a and makes the overall effect to be a linear relationship betwee

The measurements were made with the range of impinging velocit

from 5.53 to 16.62 m-s^"1. Under such range, the kcct increases from 0.577 to 1.037 s^"1, and

from 0.00641 to 0.0416 m-s^"1, showing the effect of GIS enhancing mass transfer.

4.8 Resistance of the reactor

Resistance of the device, Ap, is an important factor to be considered in selecting impinging velocity,

The data describing the effect o

measured at different liquid flow rat re shown in Fig. 18. The following can be observed from the

figure: (1) The liquid flow rate Vi has a modest influence on Ap; (2) In the whole range of

ested,the pressure drops over the reactor are small; (3) In comparison, the resistance of the GIS gas-liquid reactor used in the present study is larger than that of the solid-gas IS contactor reported previously (Wu & Wu, 1997) by about 40%. This may be due to stronger interaction between liquid and gas than between solid and gas. Similar phenomena were also observed in wet-wall or packed column etc; and (4) The influence o xhibits different tendencies before and after 10 m-s^-1. The reason

for this is not clear. One possibility is that a conversion of flow pattern may occur at this point. To balance opposed factors for both larger mass transfer coefficient and lower energy consumption, according to the data in Figs. 16 or 17 and 18, the range from 10 to 15 m-s^"1 may be an optimal window for the impinging velocit

In conclusion, an investigation was made to evaluate the desulfurization of flue gas (DFG) by absorption in a gas-continuous impinging stream gas-liquid reactor for systems involving fast reaction(s) in liquid. The following are concluded:

(l)The reactor has good global performance for DFG. Under the moderate conditions of liquid to gas flow rate ratio

m -m^~ , impinging velocity d SO₂ concentration in the feeding gas o

-3200 mg/m³, stable

operation of the reactor yields a sulfur-removal efficiency of 92.5%, with residue SO₂ in cleaned gas of 240 mg-nf ³, and the pressure drop over the reactor is only 405 Pa;

(2) The following optimal or feasible conditions and structure parameters are determined:

for pseudo flue gas without and the nozzles are mounted at the outlets of gas

conduits;

(3) The gas-film mass transfer coefficient, ko, is determined based on the Sauter mean diameter of spray droplets. The results show essentially no influence of initial concentration of SO₂ o

suggesting that the process is controlled by diffusion through gas film and that the method proposed for the determination of

is feasible; (4) The data on the relationship between impinging velocity and gas-film mass transfer coefficient are fitted b

ith the standard deviation SD=

implying

is a strong affecting variable, and thus is an important operation variable;

(5) With the impinging veloci

ranging from 5.53 to

increases from 0.577 t

nd k_G from 0.00641 to

showing the effect of GIS enhancing mass transfer.

While several embodiments of the invention have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and structures for performing the functions and/or obtaining the results or advantages described herein, and each of such variations, modifications and improvements is deemed to be within the scope of the present invention. More generally, those skilled in the art would readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that actual parameters, dimensions, materials, and configurations will depend upon specific applications for which the teachings of the present invention are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, the invention may be practiced otherwise than as specifically described. The present invention is directed to each individual feature, system, material and/or method described herein. In addition, any combination of two or more such features, systems, materials and/or methods, provided that such features, systems, materials and/or methods are not mutually inconsistent, is included within the scope of the present invention. In the claims (as well as in the specification above), all transitional phrases or phrases of inclusion, such as "comprising," "including," "carrying," "having," "containing," "composed of," "made of," "formed of," "involving" and the like shall be interpreted to be open-ended, i.e. to mean "including but not limited to" and, therefore, encompassing the items listed thereafter and equivalents thereof as well as additional items. Only the transitional phrases or phrases of inclusion "consisting of and "consisting essentially of are to be interpreted as closed or semi-closed phrases, respectively. The indefinite articles "a" and "an," as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean "at least one." The phrase "and/or," as used herein in the specification and in the claims, should be understood to mean "either or both" of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Other elements may optionally be present other than the elements specifically identified by the "and/or" clause, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, a reference to "A and/or B" can refer, in one embodiment, to A only (optionally including elements other than B); in another embodiment, to B only (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc. As used herein in the specification and in the claims, "or" should be understood to have the same meaning as "and/or" as defined above. For example, when separating items in a list, "or" or "and/or" shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as "only one of or "exactly one of," will refer to the inclusion of exactly one element of a number or list of elements. In general, the term "or" as used herein shall only be interpreted as indicating exclusive alternatives (i.e. "one or the other but not both") when preceded by terms of exclusivity, such as "either," "one of," "only one of," or "exactly one of."

In cases where the present specification and a document incorporated by reference and/or referred to herein include conflicting disclosure, and/or inconsistent use of terminology, and/or the incorporated/referenced documents use or define terms differently than they are used or defined in the present specification, the present specification shall control.

What is claimed is:

Claims

1. A reactor comprising: a reaction chamber; and at least three ejectors, each ejector comprising a spray nozzle for discharging a liquid and a gas conduit for discharging a gas, the spray nozzle and gas conduit constructed and arranged to discharge a gas-liquid mixture from the ejector, wherein the ejectors are constructed and arranged in the reactor to cause impinging of the gas-liquid mixtures in the reaction chamber.

2. A reactor as in claim 1 , wherein the at least three ejectors are arranged along a first plane intersecting side walls of the chamber.

3. A reactor as in claim 1 , wherein the liquid comprises a suspension of solid particulates.

4. A reactor as in claim 1, the outlet of a first ejector is positioned facing the outlet of a second ejector, such that gas-liquid mixtures discharged from the ejectors impinge upon one another within the reaction chamber.

5. A reactor as in claim 1 , wherein the reactor comprises at least four ejectors constructed and arranged to cause impinging of the gas-liquid mixtures in the reaction chamber.

6. A reactor as in claim 1 , wherein the reactor further comprises a second set of at least three ejectors, the second of set of ejectors arranged along a second plane intersecting side walls of the chamber, wherein the second plane is different from the first plane.

7. A reactor as in claim 1, further comprising a mesh foam remover.

8. A reactor as in claim 1 , further comprising an internal wet cyclone.

9. A reactor as in claim 1, wherein the outlet of the spray nozzle is positioned essentially at the outlet of the gas conduit.

10. A method comprising: providing a gas containing a first component and a liquid containing a second component; discharging the gas and the liquid as gas-liquid sprays or mixtures in at least three directions in a reaction chamber; causing the gas-liquid sprays or mixtures discharged from in the at least three directions to impinge upon one another near a radially central region of the reaction chamber; and causing a chemical reaction and/or chemical absorption between the first and second components in the reaction chamber.

1,1. A method as in claim 10, wherein the first and/or second component comprises a pollutant.

12. A method as in claim 11, wherein the first component comprises SOx and/or CO₂.

13. A method as in claim 12, wherein the second component comprises a base.

14. A method as in claim 13, wherein the second component comprises NaOH and/or Ca(OH)₂.

15. A method as in claim 10, further comprising recovering a product gas from the reaction chamber.

16. A method as in claim 15, wherein the product gas is less environmentally harmful than the gas provided in the providing act.

17. A method as in claim 10, further comprising recovering a product liquid from the reaction chamber.

18. A method as in claim 17, wherein the product liquid comprises a salt.

19. A method as in claim 18, wherein the product liquid comprises Na₂SO₃ and/or CaSO₃ and/or Na₂SO₄ and/or CaSO₄.

20. A method as in claim 19, wherein the product liquid is further treated to form a gaseous product.

21. A method as in claim 20, wherein the gaseous product comprises CO₂.

22. A method as in claim 21, further comprising directing the gaseous product into a photobioreactor.

23. A method as in claim 19, wherein the product liquid is reacted to form gypsum.

24. A method as in claim 10, further comprising removing particulates from the gas- liquid mixture in the reaction chamber.

25. A method as in claim 10, wherein the gas or gas-liquid mixture flows at a rate greater than about 500 m³/h.

26. A method as in claim 25, wherein the gas or gas-liquid mixture flows at a rate between about 800 m³/h and about 1000 m³/h.

27. A method as in claim 10, wherein the rate of the chemical reaction and/or chemical absorption is mass transfer limited.

28. A method as in claim 15, wherein the product gas comprises CO₂.

29. A method as in claim 28, further comprising directing the product gas into a photobioreactor.

30. A reactor comprising : a reaction chamber; at least two ejectors, each ejector comprising a spray nozzle for discharging a liquid and a gas conduit for discharging a gas, the spray nozzle and gas conduit constructed and arranged to discharge a gas-liquid spray or mixture from the ejector, wherein the ejectors are constructed and arranged in the reactor to cause impinging of the gas-liquid sprays or mixtures in the reaction chamber; and a particulate remover constructed and arranged to remove particulates from the gas-liquid mixture.

31. A method of treating a gas with a photobioreactor system comprising: passing the gas through a reactor including a reaction chamber and at least two ejectors, each ejector comprising a spray nozzle for discharging a liquid and a gas conduit for discharging a gas, the spray nozzle and gas conduit constructed and arranged to discharge a gas-liquid spray or mixture from the ejector, wherein the ejectors are constructed and arranged in the reactor to cause impinging of the gas-liquid sprays or mixtures in the reaction chamber, and wherein the reactor is in fluid communication with the photobioreactor; at least partially removing from the gas at least one substance selected from the group consisting of SOx, NOx, CO₂, and solid particulates in the reactor; passing the gas through the photobioreactor; and at least partially removing from the gas at least one substance selected from the group consisting of NOx and CO₂ in the photobioreactor.

32. A gas treatment system comprising: a photobioreactor; and a reactor including a reaction chamber and at least two ejectors, each ejector comprising a spray nozzle for discharging a liquid and a gas conduit for discharging a gas, the spray nozzle and gas conduit constructed and arranged to discharge a gas-liquid spray or mixture from the ejector, wherein the ejectors are constructed and arranged in the reactor to cause impinging of the gas-liquid mixtures in the reaction chamber.