Field of the Invention

The present invention generally relates to the fueling of pyrohydrolysis reactors. More specifically, the present invention relates to novel fuel compositions that can be advantageously utilized to distribute inexpensive fuels throughout a fluid bed reactor.

Background of the Invention

Metal chloride pyrohydrolysis is an important part of many chloride based flow sheets. Metal chloride pyrohydrolysis is used to recover the hydrochloric acid ("HCl") from metal chloride solutions, for reuse. The metal chloride solutions may contain chlorides of metals such as iron, nickel, magnesium, calcium, cobalt, and titanium. The most common example is the steel pickling plant, where the cleaning agent (that is, HCl) is recovered from iron chloride solutions. In hydrometallurgy, metal chloride pyrohydrolysis is finding more applications, most notably for nickel beneficiation and for synthetic rutile production. The key reaction for recovering HCl is the pyrohydrolysis of the metal chloride. The core unit in a pyrohydrolysis plant (a "pyrohydrolyser") is a high temperature roaster (or pyrohydrolysis reactor) for evaporating water and converting the metal chlorides to metal oxides. Pyrohydrolysis reactors for roasting of metal chloride solutions can be either spray roasters or fluid bed roasters. Both types of roasters rely on direct heat transfer from the combustion of hydrocarbon fuels to maintain the required elevated temperature for evaporation and reaction in a reactor. It should be understood that the phrase "fluid bed reactor" used herein, means a fluid bed roaster used for performing pyrohydrolysis reactions. Generally, fluid bed reactors are fueled by natural gas. The gas enters via the bottom and the gas is evenly distributed via nozzle injectors. Although natural gas or other gaseous fuels work well in a fluid bed reactor, the price of natural gas represents a significant operating expense for the reactor. Summary of the Invention A novel fuel composition suitable for fueling fluid bed reactors has been discovered. The fuel composition comprises a mixture of a combustible base, a densifying component, and a binder. By applying pressure to the fuel composition, a briquette can be formed that is stable in the fluid bed reactor. The amount of densifying component can be adjusted to produce briquettes that exhibit neutral density in the fluid bed. At neutral density the briquettes will mix throughout the fluid bed. If desired, higher levels of densifying component can be utilized to make briquettes that sink in the fluid bed such that they remain in the combustion zone of the fluid bed. The fuel compositions of the present invention allow the use of inexpensive fuels as the combustible base, such as waste petroleum coke and coal.

Description of the Drawings

The present invention is illustrated by way of example in the following drawing in which like references indicate similar elements. The following drawing discloses various embodiments of the present invention for purposes of illustration only. The drawing is not intended to limit the scope of the invention. FIG. 1 illustrates an example of a fluid bed reactor.

Detailed Description of Preferred Embodiments of the Invention

In the following detailed description of preferred embodiments of the present invention, reference is made to the accompanying Drawing, which forms a part hereof, and in which is shown by way of illustration specific embodiments in which the present invention may be practiced. It should be understood that other embodiments may be utilized and changes may be made without departing from the scope of the present invention. A pyrohydrolysis plant consists of a high temperature reactor (that is, a pyrohydrolysis reactor) for evaporating water and converting the metal chlorides to metal oxides. The metal oxides are typically recovered from the bottom of the reactor as hard and dense particles. The reactor is normally equipped with an extensive off- gas system, including dust removal equipment (for example, a cyclone), a gas/liquid contactor (for example, a venturi) for partial evaporation of the fresh feed, and an absorber for recovering the gaseous HCl. The key regeneration reaction in a pyrohydrolysis reactor is the pyrohydrolysis of metal chloride. Fuel combustion provides the required energy for evaporation and pyrohydrolysis reactions in the reactor. The following reactions are shown for a natural gas burning unit, treating a bi-valent metal chloride. CH4 + 2O2 "» CO2 + 2 H2O (g) (1) MeCl2 + H2O ■» MeO + 2HCl (g) (2) H2O (1) -» H2O (g) (3) Figure 1 shows a diagram of a fluid bed reactor 100. The metal chloride solution 102 is introduced into a large bed of hot metal oxides 104. The required energy is provided directly by the combustion of fuel 106. Air 108 can be introduced via a separate duct as in Figure 1 or a premixed stream of air and fuel can be introduced. A fraction containing metal oxide sinks to the bottom of the reactor 100 and is removed from the bottom of the reactor 100. A fraction containing off-gases 112, including HCl, are removed via the top of the reactor 100. A pyrohydrolysis plant is very energy intensive, mainly because a large amount of fuel combustion is required to evaporate the metal chloride solution and to heat the reactor contents. In fluid bed reactors, the gas and solids are fully mixed and their exit temperature is normally 700 0C to 900 0C. For fluid bed reactors, it is important to have the heat of combustion generated in the lower part of the fluid bed to assure even heat distribution throughout the reactor. Generally, the fuel is a gas that is introduced at the bottom of the reactor and evenly distributed via numerous injection nozzles or burners. Although natural gas or other gaseous fuels work well in a fluid bed pyrohydrolysis reactor, the price of the gas fuels represents a significant operating expense for the reactor. By experimentation, a novel fuel composition has been discovered that is suitable for fueling fluid bed reactors. The novel fuel compositions of the present invention are less expensive than the gas fuels of the prior art, resulting in significant cost savings. Fuel compositions of the present invention generally comprise a mixture of a combustible base, a densifying component, and a binder. By applying pressure to the fuel composition, a briquette can be formed that is stable in the fluid bed reactor. Typically, the fuel composition will comprise at least about 5 percent by weight of binder. Additionally, the fuel composition will typically comprise no more than about 10 percent by weight of binder. The amount of densifying component can be adjusted to produce briquettes that exhibit neutral density in the fluid bed. At neutral density the briquettes will mix throughout the fluid bed. If desired, higher levels of densifying component can be utilized to make briquettes that sink in the fluid bed such that they remain in the combustion zone of the fluid bed. The fuel briquettes according to the present invention can be introduced into the fluid bed in any manner suitable for the particular reactor being utilized. The fuel compositions of the present invention allow the use of inexpensive fuels as the combustible base, such as waste petroleum coke and coal. In one embodiment of the present invention, calcined petroleum coke was advantageously utilized as the combustible base. The present invention contemplates the use of other carbon sources, such as green petroleum coke, coals, and off-spec carbon black, for example. The combustible base may comprise a single fuel source or may comprise a mixture of two or more fuel sources. The densifying component is typically a metal oxide. However, other densifying components may be utilized in amounts sufficient to cause the fuel briquettes to mix throughout the fluid bed or to sink to the bottom of the fluid bed as needed. Preferably, the densifying component comprises the same metal oxide as that which is recovered from the pyrohydrolysis reactor. For example, if the pyrohydrolysis reactor is producing iron oxide then iron oxide will be the preferred densifying component in fuel briquettes used for fueling the pyrohydrolysis reactor. More preferably, the metal oxide used as the densifying component will be metal oxide that is recycled from the metal oxide that is recovered from the same pyrohydrolysis reactor to be fueled by the fuel briquettes. For example, some of the iron oxide recovered from a pyrohydrolysis reactor can be used as a densifying component in fuel briquettes used to continue fueling the pyrohydrolysis reactor. Fuel briquettes of the present invention can be produced by first mixing the combustible base, the densifying component, and the binder to produce a fuel composition. The amount of pressure applied and the duration for which the pressure is applied to form fuel briquettes may vary somewhat depending on the specific composition of the fuel briquettes. Typically, a pressure of at least about 500 psi (35.15 kg-force/sq. cm) is applied to the fuel composition to form a fuel briquette. However, pressures up to about 600,000 psi (42,184 kg-force/sq. cm) may be utilized in embodiments of the present invention. The needed pressure can be applied using a commercial briquetting machine, for example. Typically, the pressure is applied for a few seconds. A pressure of about 1000 psi (70.3 kg-force/sq. cm) has been successfully utilized in producing fuel briquettes. After the pressure is applied, the fuel briquettes may be heated to dry the briquettes. Although the heating step is not necessary, drying the briquettes by heating will typically reduce the heat load of the fluid bed. When heating, the specific temperature applied and the duration for which the temperature is applied may vary somewhat depending on the specific composition of the fuel briquettes. For example, fuel briquettes may be subjected to air drying or thermal drying at temperatures of 200 0C or more. Fuel briquettes have been successfully produced by heating them overnight at a temperature of about 100 °C. Fuel briquettes produced in accordance with the present invention will preferably have a crush strength of at least about 15 lbs (6.80 kg). Fuel briquettes produced in accordance with the present invention will preferably have a crush strength of no more than about 1000 lbs (453.59 kg).

Examples In accordance with the present invention, fuel briquettes were produced using petroleum coke as the combustible base and iron oxide as the densifying component. Molasses and bentonite were used as the binder. The fuel composition was produced by mixing 5 lbs (2.27 kg) of iron oxide, 5 lbs (2.27 kg) of petroleum coke, 2.5 lbs (1.13 kg) of molasses, and 0.5 Ib (0.23 kg) of bentonite. A pressure of 1000 psi (70.3 kg-force/sq. cm) was applied for a few seconds. Twenty briquettes were produced from the fuel composition and the briquettes were dried overnight at a temperature of 100 0C. The briquettes were weighed and submitted for crush strength tests and density measurements. The briquettes ranged in weight from a minimum of 12.64 g to a maximum of 13.5O g with an average weight of 13.19 g. The briquettes ranged in crush strength from a minimum of 78 lbs (35.38 kg) to a maximum of 140 lbs (63.5 kg) with an average crush strength of 100.5 lbs (45.59 kg). The briquettes had an average density of 1.93 g/cm3. Other samples of fuel briquettes were produced and tested in a similar manner as described above except the binder comprised molasses and calcium hydroxide. Four different fuel compositions were used to produce the briquettes. Sample 1 was produced by mixing 5 lbs (2.27 kg) iron oxide pellets, 5 lbs (2.27 kg) petroleum coke, 0.25 Ib (113.4 g) molasses, and 0.05 Ib (22.68 g) calcium hydroxide. Sample 2 was produced by mixing 4 lbs (1.81 kg) iron oxide pellets, 6 lbs (2.72 kg) petroleum coke, 0.30 Ib (136.08 g) molasses, and 0.06 Ib (27.22 g) calcium hydroxide. Sample 3 was produced by mixing 6 lbs (2.72 kg) iron oxide pellets, 4 lbs (1.81 kg) petroleum coke, 0.20 Ib (90.72 g) molasses, and 0.04 Ib (18.14 g) calcium hydroxide. Sample 4 was produced by mixing 5 lbs (2.27 kg) iron oxide pellets, 5 lbs (2.27 kg) petroleum coke, 0.50 Ib (0.23 kg) molasses, and 0.10 Ib (45.36 g) calcium hydroxide. Table 1 shows the results of the crush strength test and the density measurement on briquettes made from the four different fuel compositions.

Table 1

In accordance with the present invention fuel briquettes have been produced that are suitable for fueling pyrohydrolysis reactors. The briquettes allow inexpensive fuels to be utilized instead of more expensive fuels currently used, such as natural gas, resulting in significant cost savings. While the present invention has been described in detail with respect to specific embodiments thereof, it will be appreciated that those skilled in the art, upon attaining an understanding of the foregoing, may readily conceive of alterations to, variations of and equivalents to these embodiments. Accordingly, the scope of the present invention should be assessed as that of the appended claims and by equivalents thereto.