Process and apparatus for slaking lime and dissolving scale

• US 9,650,293 B2
• Filed: 03/30/2015
• Issued: 05/16/2017
• Est. Priority Date: 03/05/2010
• Status: Active Grant

• Current Assignee: RDP Technologies Incorporated
• Original Assignee: RDP Technologies Incorporated
• Inventors: Christy, Richard W., Quici, Michael, Litz, Louis
• Primary Examiner(s): Young, Natasha
• Application Number:
  US14/673,099
• Publication Number:
  US 20150203386A1
• Time in Patent Office: 778 Days
• CPC Class Codes: C02F 1/008 Control or steering systems not provided for elsewhere in subclass C02F
• CPC Class Codes: C02F 1/529 Processes or devices for preparing lime water
• CPC Class Codes: C02F 1/66 by neutralisation; pH adjustment for degassing C02F1/20; using ion-exchange C02F1/42; for flocculation or precipitation of suspended impurities C02F1/52; for removing dissolved compounds C02F1/58
• CPC Class Codes: C02F 1/687 Devices for dosing solid compounds
• CPC Class Codes: C02F 2209/005 Processes using a programmable logic controller [PLC]
• CPC Class Codes: C02F 2209/02 Temperature
• CPC Class Codes: C02F 2303/04 Disinfection
• CPC Class Codes: C02F 2303/22 Eliminating or preventing deposits, scale removal, scale prevention C02F1/042, C02F1/4602, C02F5/00 take precedence
• CPC Class Codes: C04B 2/04 Slaking simultaneous dehydrating of gypsum and slaking of lime C04B11/022
• CPC Class Codes: C04B 2/066 Making use of the hydration reaction, e.g. the reaction heat for dehydrating gypsum; Chemical drying by using unslaked lime
• CPC Class Codes: C04B 2/08 Devices therefor

Abstract

Process and apparatus is disclosed for providing a chemical reaction between calcium oxide containing grit particles to produce calcium hydroxide and heat, capturing the heat of hydration and using it to preheat water initially at ambient temperature, to rise to an elevated temperature to increase the amount of lime present in the water to a supersaturated lime suspension level, with the chemical reaction running to completion, followed by cooling. Heat from a water jacket may be used to raise the temperature in the lime slaker.

Claims

1. A process for producing slaked lime slurry comprising the steps of:

providing a slaking vessel having at least one support location that is provided with at least one load cell, wherein the load cell provides a signal indicative of a total weight of the slaking vessel and its contents;

charging a predetermined weight of water to the slaking vessel by using the signal from the load cell to stop charging water to the slaking vessel when the signal from the load cell indicates that the predetermined weight of water has been charged to the slaking vessel, wherein the water has a temperature;

charging a predetermined weight of lime feed stock to the slaking vessel by using the signal from the load cell to stop charging lime feed stock to the slaking vessel when the signal from the load cell indicates that the predetermined weight of lime feed stock has been charged to the slaking vessel, wherein the lime feed stock comprises calcium oxide (CaO), and wherein said step of charging a predetermined weight of lime feed stock to the slaking vessel is performed after said step of charging a predetermined weight of water to the slaking vessel is completed;

allowing the calcium oxide to undergo a slaking reaction with the water in the slaking vessel at least until the slaking reaction substantially reaches completion,

wherein the predetermined weight of water charged to the slaking vessel is in excess of the weight of water required by stoichiometry of the slaking reaction for hydration of all the calcium oxide in the predetermined weight of lime feed stock charged to the slaking vessel;

controlling the temperature of the water such that the water is at a temperature within a predetermined range before the lime feed stock is charged to the slaking vessel, the predetermined temperature range of the water being selected such that the contents of the slaking vessel are at a temperature in the range of 175°

F. to 195°

F. (79 degrees C. to 91 degrees C.) at least when the slaking reaction substantially reaches completion, and wherein no cooling or dilution water is added to the contents of the slaking vessel after said step of charging a predetermined weight of water to the slaking vessel and before the slaking reaction substantially reaches completion; and

discharging the slaked lime slurry from the slaking vessel after the slaking reaction substantially reaches completion.

2. The process for producing slaked lime slurry according to claim 1, wherein the contents of the slaking vessel are at a temperature in the range of 160°

F. to 212°

F. (71 degrees C. to 100 degrees C.) at least when the slaking reaction substantially reaches completion.

3. The process for producing slaked lime slurry according to claim 1, wherein the lime feed stock comprises at least 90 percent calcium oxide (CaO) and at least some grit but not exceeding 10 percent grit.

4. The process for producing slaked lime slurry according to claim 1, wherein the weight of lime feed stock charged to the slaking vessel is 5 percent to 45 percent of the total weight of the water and the lime feed stock charged to the slaking vessel.

5. The process for producing slaked lime slurry according to claim 1, wherein the weight of water and the weight of lime feed stock charged to the slaking vessel are in a ratio selected such that a slaked lime slurry resulting from the weight of water and the weight of lime feed stock charged to the slaking vessel is suitable for use in one or more target applications without dilution of the slaked lime slurry by adding water to the slaked lime slurry after the slaking reaction substantially reaches completion.

6. The process for producing slaked lime slurry according to claim 1, wherein the temperature of the water before the lime feed stock is charged to the slaking vessel, is controlled to be within a range of 50°

F. to 80°

F.

7. The process for producing slaked lime slurry according to claim 1, further comprising the steps of:

providing a slurry aging tank;

providing a grit separation device to remove grit from the slaked lime slurry;

providing a discharge line for circulating slaked lime slurry from the slurry aging tank to the grit separation device, wherein the discharge line passes through one or more dosing locations;

providing a return line from the grit separation device to the slurry aging tank;

conveying the slaked lime slurry from the slaking vessel to the slurry aging tank after the slaking reaction has substantially reached completion;

circulating slaked lime slurry from the slurry aging tank to the grit separation device and returning the slaked lime slurry from the grit separation device to the slurry aging tank to remove grit from the slaked lime slurry; and

providing a dosing sub-system to deliver a controlled amount of slaked lime slurry at each dosing location as needed under the control of an operator or a controller.

8. The process for producing slaked lime slurry according to claim 7, further comprising the steps of:

repeating said step of controlling the temperature of the water such that the water is at a temperature within a predetermined range before the lime feed stock is charged to the slaking vessel, said step of charging a predetermined weight of water to the slaking vessel, said step of charging a predetermined weight of lime feed stock to the slaking vessel, said step of allowing the calcium oxide to undergo a slaking reaction with the water in the slaking vessel, said step of discharging the slaked lime slurry from the slaking vessel, and said step of conveying the slaked lime slurry from the slaking vessel to the slurry aging tank, in order to provide one or more subsequent batches of slaked lime slurry to the slurry aging tank to ensure that there is an adequate supply of slaked lime slurry in the slurry aging tank as required.

9. The process for producing slaked lime slurry according to claim 8, further comprising the steps of:

providing a jacket around the slaking vessel;

cooling the contents of the slaking vessel prior to said step of discharging the slaked lime slurry from the slaking vessel by providing water within the jacket; and

using the water from the jacket to provide at least in part the weight of water charged to the slaking vessel for producing one of the one or more subsequent batches of slaked lime slurry.

10. The process for producing slaked lime slurry according to claim 9, further comprising the steps of:

providing a jacket around the slurry aging tank; and

arranging for the water provided within the jacket of the slaking vessel to pass through the jacket of the slurry aging tank.

11. The process for producing slaked lime slurry according to claim 7, wherein said step of providing a dosing sub-system comprises the steps of:

providing a dosing subsystem line in communication with the discharge line and extending to a dosing discharge at a respective dosing location;

providing a first valve in the dosing sub-system line;

providing a grit trap between the first valve and the dosing discharge;

providing a flowmeter between the grit trap and the dosing discharge; and

providing a pinch valve between the flowmeter and the dosing discharge.

12. The process for producing slaked lime slurry according to claim 1, wherein a mixture resulting from the weight of water and the weight of lime feed stock charged to the slaking vessel and including reaction products thereof, at any time after said step of charging a predetermined weight of lime feed stock to the slaking vessel and before said step of discharging the slaked lime slurry from the slaking vessel, forms the contents of the slaking vessel, the process for producing slaked lime slurry further comprising the steps of:

monitoring the temperature of the contents of the slaking vessel using a temperature sensing device; and

determining that the slaking reaction has substantially reached completion when the temperature of the contents of the slaking vessel is not increasing over a predetermined time period.

13. The process for producing slaked lime slurry according to claim 1, further comprising the steps of:

providing a heater for heating at least part of the weight of water to be charged to the slaking vessel; and

providing a water temperature sensing device to sense the temperature of the weight of water charged to the slaking vessel, and

wherein said step of controlling the temperature of the water such that the water is at a temperature within a predetermined range before the lime feed stock is charged to the slaking vessel comprises the steps of;

monitoring the temperature of the water being charged to the slaking vessel; and

heating at least part of the water to be charged to the slaking vessel to ensure that the weight of water charged to the slaking vessel is at a temperature within the predetermined temperature range.

14. An apparatus for producing slaked lime slurry comprising:

a programmable control system;

a slaking vessel having at least one support location that is provided with at least one load cell, wherein the load cell provides a load cell signal indicative of a total weight of the slaking vessel and its contents, said load cell communicating with said programmable control system such that said load cell signal can be received by said programmable control system;

slaking vessel temperature sensing means for sensing the temperature of the contents of said slaking vessel, wherein said slaking vessel temperature sensing means provides a slaking vessel temperature signal indicative of the temperature of the contents of said slaking vessel, said slaking vessel temperature sensing means communicating with said programmable control system such that said slaking vessel temperature signal can be received by said programmable control system;

means for charging water into the slaking vessel, said programmable control system communicating with said means for charging water into the slaking vessel, said programmable control system stopping the charging of water into said slaking vessel when said load cell signal indicates that a predetermined weight of water has been charged into said slaking vessel, wherein the water charged into said slaking vessel has a temperature;

means for mixing the content of said slaking vessel;

water temperature control means for controlling the temperature of the water charged into said slaking vessel, said water temperature control means communicating with said programmable control system, said programmable control system controlling said water temperature control means such that the temperature of the water charged into said slaking vessel is within a predetermined water temperature range;

means for charging lime feed stock into the slaking vessel, said programmable control system communicating with said means for charging lime feed stock into the slaking vessel, said programmable control system stopping the charging of lime feed stock into said slaking vessel when said load cell signal indicates that a predetermined weight of lime feed stock has been charged into said slaking vessel, thereby allowing a slaking reaction to take place; and

means for discharging the contents of said slaking vessel;

said programmable control system communicating with said means for discharging the contents of said slaking vessel, said programmable control system monitoring the temperature of the contents of said slaking vessel using said slaking vessel temperature signal, said programmable control system operating said means for discharging the contents of said slaking vessel to discharge the contents of said slaking vessel when the temperature of the contents of said slaking vessel remains within a predetermined temperature range for a predetermined period of time;

wherein said programmable control system controls the temperature of the water charged into said slaking vessel such that the contents of said slaking vessel will be at a temperature in the range of 180°

F. to 195°

F. (82 degrees C. to 91 degrees C.) at least when the slaking reaction substantially reaches completion, said programmable control system determining the temperature range for the water to be charged to said slaking vessel using at least the predetermined weight of the water to be charged to said slaking vessel and the predetermined weight of the lime feed stock to be charged to said slaking vessel, wherein said programmable control system operates said water temperature control means such that the water temperature of the water charged to said slaking vessel is initially within the water temperature range determined by said logic means before the lime feed stock is charged to the slaking vessel;

wherein said water temperature control means comprises a heater supplied with energy from an auxiliary energy source.

15. The apparatus according to claim 14, wherein the slaking reaction generates heat, wherein said slaking vessel has a jacket surrounding an inner compartment where the contents of the slaking vessel are held at least during the slaking reaction, and wherein said water temperature control means further comprises:

piping and one or more valves controlled by said programmable control system to direct at least a portion of the water to be charged to said slaking vessel into and out of said jacket to thereby recover at least a part of the heat generated by the slaking reaction and at least reduce the energy required for heating water by said heater;

piping for directing water from said jacket to said heater;

piping and valves for directing one of water from a process water supply source, water from said heater, and a mixture thereof to said slaking vessel.

16. The apparatus according to claim 15, wherein the contents of said slaking vessel after the slaking reaction substantially reaches completion is in the form of a slaked lime slurry, wherein a slurry aging tank is provided and said slurry aging tank has a jacket surrounding an inner compartment where the slaked lime slurry is stored, and wherein the at least a portion of the water to be charged to said slaking vessel is directed into and out of said jacket of said slurry aging tank before it is directed into said jacket of said slaking vessel.

17. A process of slaking lime in batches comprising the steps of:

(a) providing valves and piping to supply water at an ambient water temperature to a lime slaker;

(b) providing water to the lime slaker;

(c) providing calcium oxide and grit particles to the lime slaker after said step of providing water to the lime slaker;

(d) allowing a chemical reaction to take place, whereby the calcium oxide and water combine to produce calcium hydroxide and heat in an exothermic reaction in the lime slaker;

(e) providing a heating device for preheating water to an elevated temperature above an ambient water temperature, wherein the heating device uses an energy source other than heat from the exothermic chemical reaction of said step of allowing a chemical reaction;

(f) capturing heat of hydration from the exothermic reaction by providing a jacket around the lime slaker and passing water through the jacket;

(g) supplying water from the jacket to the heating device, wherein said step of providing water to the lime slaker comprises supplying water from the heating device to the lime slaker;

(h) controlling the heat supplied to the water from the jacket by the heating device, controlling the amount of water passing from the heating device to the lime slaker, controlling an amount of water at ambient temperature supplied to the lime slaker, and controlling an amount of calcium oxide and grit particles supplied to the lime slaker, at least based upon;

(A) the temperature of the water in the lime slaker prior to said step of providing calcium oxide and grit particles to the lime slaker; and

(B) a predetermined hydration reaction temperature; and

(i) allowing the chemical reaction to run to completion.

18. An apparatus for carrying out a process for producing slaked lime slurry in accordance with claim 17, the apparatus comprising:

a programmable control system;

a slaking vessel having at least one support location that is provided with at least one load cell, wherein the load cell provides a load cell signal indicative of a total weight of the slaking vessel and its contents, said load cell communicating with said programmable control system such that said load cell signal can be received by said programmable control system;

slaking vessel temperature sensing means for sensing the temperature of the contents of said slaking vessel, wherein said slaking vessel temperature sensing means provides a slaking vessel temperature signal indicative of the temperature of the contents of said slaking vessel, said slaking vessel temperature sensing means communicating with said programmable control system such that said slaking vessel temperature signal can be received by said programmable control system;

means for charging water into the slaking vessel, said programmable control system communicating with said means for charging water into the slaking vessel, wherein the water charged into said slaking vessel has a temperature;

means for mixing the content of said slaking vessel;

water temperature control means for controlling the temperature of the water charged into said slaking vessel, said water temperature control means communicating with said programmable control system, said programmable control system controlling said water temperature control means such that the temperature of the water charged into said slaking vessel is within a predetermined water temperature range, wherein said water temperature control means comprises a heater supplied with energy from an auxiliary energy source;

means for charging lime feed stock into the slaking vessel, said programmable control system communicating with said means for charging lime feed stock into the slaking vessel, said programmable control system operating said means for charging lime feed stock into the slaking vessel to charge lime feed stock into said slaking vessel, thereby allowing a slaking reaction to take place; and

means for discharging the contents of said slaking vessel;

said programmable control system communicating with said means for discharging the contents of said slaking vessel, said programmable control system monitoring the temperature of the contents of said slaking vessel using said slaking vessel temperature signal, said programmable control system operating said means for discharging the contents of said slaking vessel to discharge the contents of said slaking vessel when the temperature of the contents of said slaking vessel remains within a predetermined temperature range for a predetermined period of time indicative of the completion of the slaking reaction.