Heater control

• US 6,023,052 A
• Filed: 11/04/1998
• Issued: 02/08/2000
• Est. Priority Date: 11/07/1997
• Status: Expired due to Term

• Current Assignee: Shell Oil Company (Shell Plc)
• Original Assignee: Shell Oil Company (Shell Plc)
• Inventors: Savage, William Mountjoy, Burnett, Robert Rex, Carl, Frederick Gordon Jr.
• Primary Examiner(s): PASCHALL, MARK H
• Application Number:
  US09/185,881
• Time in Patent Office: 461 Days
• Field of Search: 219/483-486, 219/501, 219/508, 219/507, 219/494, 307/39-41, 340/310.01, 340/310.02
• US Class Current: 219/483
• CPC Class Codes: G05D 23/1913 delivering a series of pulses
• CPC Class Codes: G05D 23/1931 to control the temperature of one space
• CPC Class Codes: G05D 23/1934 each space being provided with one sensor acting on one or more control means
• CPC Class Codes: H05B 1/0247 For chemical processes

Abstract

A method and apparatus are provided for controlling parallel heater elements, the method including the steps of: providing a plurality of electrical heater elements; generating a plurality of temperature signals associated with a plurality of the heater elements; generating a control signal based on one or more temperature signals; providing an alternating current power supply connected to the electrical heater elements through a power transmission system; generating a signal when the voltage of the alternating current power supply passes through ground potential; blocking electrical power to a heater element starting when a zero detection signal is detected an ending when another zero detection signal is detected, for a fraction of the alternating current cycles in a time period, the fraction being a function of the control signal; and transmitting temperature control signals through the power transmission system.

Claims

1. A control system for controlling parallel heater elements comprising:

a plurality of electrical heater elements;

a plurality of temperature sensors associated with a plurality of the heater elements, the temperature sensors effective to generate temperature signals;

at least one temperature controller effective to generate a control signal based on at least one temperature signal;

an alternating current power supply connected to the electrical heater elements through a power transmission system;

a zero detection circuit effective to generate a signal when the voltage of the alternating current power supply passes through ground potential;

a firing controller that will block electrical power to a heater element, starting when a zero detection signal is detected an ending when another zero detection signal is detected, for a fraction of the alternating current cycles in a time period, the fraction being a function of the control signal;

a remote modem in the proximity of the heater elements effective to convert the temperature signals to signals transmitted through the power transmission system and to detect a control signal transmitted through the power transmission system; and

a master modem effective to convert the control signal to a signal transmitted through the power transmission system and to detect temperature signals transmitted through the power transmission system.

2. The system of claim 1 wherein a plurality of controllers are provided, each controller controlling a different heating element.

3. The system of claim 1 wherein the master modem and the remote modem communicate over an oscillating carrier signal.

4. The system of claim 1 wherein the master modem ques the remote modem to provide specific information.

5. The system of claim 4 further comprising a computer, the computer connected to the master modem and effective to determine a control signal for control of a temperature signal.

6. The system of claim 5 wherein the computer selects a maximum temperature signal associated with each heater controller, and controls that maximum temperature.

7. The system of claim 1 further comprising a multiplexing element to which a plurality of temperature inputs are connected, and from which multiplexing element digital temperature signals are provided to the remote modem.

8. The system of claim 7 wherein the digital temperature signals are provided as a series of digital data.

9. The system of claim 8 further comprising a rectifier to provide direct current to the heater elements from the firing controller.

10. The system of claim 1 wherein each individual heater element has a separate firing controller.

11. A method for controlling parallel heater elements, the method comprising the steps of:

providing a plurality of electrical heater elements;

generating a plurality of temperature signals associated with a plurality of the heater elements;

generating a control signal based on one or more temperature signals;

providing an alternating current power supply connected to the electrical heater elements through a power transmission system;

generating a signal when the voltage of the alternating current power supply passes through ground potential;

blocking electrical power to a heater element starting when a zero detection signal is detected an ending when another zero detection signal is detected, for a fraction of the alternating current cycles in a time period, the fraction being a function of the control signal; and

transmitting control signals through the power transmission system.

12. The method of claim 11 wherein a control signal is generated for each heating element.

13. The method of claim 11 wherein the temperature control signal is transmitted by an oscillating carrier signal.

14. The method of claim 11 wherein the temperature signals are transmitted to a temperature controller over power transmission system.

15. The method of claim 14 further wherein the control signal is generated by a computer, the computer effective to determine a control signal for control of a temperature signal.

16. The method of claim 15 wherein the computer selects a maximum temperature signal associated with each heater controller, and controls that maximum temperature.

17. The method of claim 11 further comprising multiplexing temperature signals associated with each heater element to provide a signal series of signals repeating digitalized temperature signals.

18. The method of claim 11 wherein the heater elements are heaters within wellbores for heating soil or rock formations.

19. The method of claim 18 wherein the heater elements are in wellbores for heating oil shale for extraction of hydrocarbons from the oil shale.

20. The method of claim 11 wherein the heaters are positioned to heat soil for removal of contaminates from the soil.