FURNACE CONTROL METHOD

Abstract

A method is described for controlling a furnace containing a plurality of catalyst-containing tubes heated by a combustion gas generated by a plurality of burners, said method comprising the steps of: (i) measuring path-averaged combustion gas temperatures on multiple paths through the furnace using tunable diode laser absorption spectroscopy, (ii) periodically measuring temperatures of surfaces within the furnace to obtain periodic surface temperature information, (iii) entering the path-averaged combustion gas temperatures and periodic surface temperature information into a computer model of the furnace, said model comprising parameters for controlling the furnace; and (iv) using the computer model and the temperature information to obtain optimised parameters for controlling the furnace. A system for performing the method is also described.

Claims

1. A method for controlling a furnace containing a plurality of catalyst-containing tubes heated by a combustion gas generated by a plurality of burners, said method comprising the steps of: (i) measuring path-averaged combustion gas temperatures on multiple paths through the furnace using tunable diode laser absorption spectroscopy, (ii) periodically measuring temperatures of surfaces within the furnace to obtain periodic surface temperature information, (iii) entering the path-averaged combustion gas temperatures and periodic surface temperature information into a computer model of the furnace, said model comprising parameters for controlling the furnace; and (iv) using the computer model and the temperature information to obtain optimised parameters for controlling the furnace.

2. The method according to claim 1 wherein the furnace is a fired steam reformer.

3. The method according to claim 1 wherein the surfaces include surfaces of the catalyst-containing tubes.

4. The method according to claim 1 wherein the path-averaged combustion gas temperatures are measured continuously during operation of the furnace.

5. The method according to claim 1 wherein the tunable diode laser absorption spectroscopy is performed using a tunable diode laser system comprising a tunable diode laser sending unit and a detector.

6. The method according to claim 1 wherein the tunable diode laser absorption spectroscopy additionally provides information on the combustion gas composition that is entered into the computer model.

7. The method according to claim 1 wherein the periodic surface temperature information is measured using a gold-cup pyrometer, an optical point pyrometer, or a thermal imaging camera.

8. The method according to claim 1 wherein the optimised parameters are used to adjust one or more of the plurality of burners, or to adjust the feed to the catalyst-containing tubes or to adjust other systems of the furnace.

9. A system for controlling a furnace containing a plurality of catalyst-containing tubes heated by a combustion gas generated by a plurality of burners, said system comprising (i) tunable diode laser absorption spectroscopy apparatus configured to provide path-averaged combustion gas temperatures on multiple paths through the furnace, (ii) temperature measurement apparatus configured to periodically measure temperatures of surfaces within the furnace to obtain periodic surface temperature information, (iii) a computer model of the furnace, said model comprising parameters for controlling the furnace; and (iv) a controller for controlling the furnace using optimised parameters provided by the computer model.

10. The system according to claim 9 wherein the furnace is a fired steam reformer.

11. The system according to claim 9 wherein the surfaces include surfaces of the catalyst-containing tubes.

12. The system according to claim 9 wherein the tunable diode laser absorption apparatus comprises a tunable diode laser sending unit and a detector.

13. The system according to claim 9 wherein the temperature measurement apparatus is selected from a gold-cup pyrometer, an optical point pyrometer, or a thermal imaging camera.

14. The method according to claim 9 wherein the controller is configured to adjust one or more of the plurality of burners, or to adjust the feed to the catalyst-containing tubes or to adjust other systems of the furnace.

15. The method according to claim 1 wherein the periodic surface temperature information is measured using a thermal imaging camera.

16. The system according to claim 9 wherein the temperature measurement apparatus is a thermal imaging camera.

Description

[0044] The invention will now be further described by reference to the drawings in which:

[0045] FIG. 1 is a depiction of a system according to the present invention.

[0046] It will be understood by those skilled in the art that the drawings are diagrammatic and that further items of equipment such as feedstock drums, pumps, vacuum pumps, compressors, gas recycling compressors, temperature sensors, pressure sensors, pressure relief valves, control valves, flow controllers, level controllers, holding tanks, storage tanks and the like may be required in a commercial plant. Provision of such ancillary equipment forms no part of the present invention and is in accordance with conventional chemical engineering practice.

[0047] In FIG. 1 there is a horizontal cross-section of a fired steam reformer furnace 10 containing rows of vertical catalyst-containing tubes 12. The tubes are fed with a mixture of hydrocarbon and steam that is reformed over a steam reforming catalyst disposed within the tubes to form synthesis gas. Whereas twenty-four tubes are depicted in three rows, typically the reformer will comprise hundreds of tubes in tens of rows. The tubes 12 are heated by a plurality of burners 14 that combust a fuel gas with air fed by feed lines 16. The feed lines are controlled by a controller 18, which opens and closes valves (not shown). The controller 18 is fed with a series of input instructions from an operator or plant control system 20.

[0048] The furnace 10 is fitted with a TDLAS system comprising a TDLAS laser controller 22 that controls a plurality of laser sources 24 attached to the exterior wall of the furnace. The laser sources 24 emit beams of laser light along a plurality of paths 26 through the furnace 10 between the rows of tubes 12 and between the rows of tubes and interior walls of the furnace. The laser light interacts with components of the combustion gas and is detected by a plurality of detectors 28 located on the furnace wall opposite the sources 24. The detectors 28 are connected to a processing unit 30 that processes the output from the detectors to provide TDLAS temperature information 32 for each of the paths 26.

[0049] The TDLAS temperature information 32 is provided to a computer model programmed into a computer 34. The model in the computer is also fed with furnace operating parameters 36 including the flowrate, temperature, pressure, and composition of the combustion fuel, combustion air, furnace tube feed gas, catalyst properties, and furnace properties.

[0050] The method and system further include a thermal imaging camera 38 directed through one or more inspection ports 40 present in the walls of the furnace 10. The thermal imaging camera captures a plurality of digital thermal images of surfaces within the furnace, including surfaces of the tubes 12. The position of the thermal imaging camera 38 is adjusted, for example as depicted by the arrow, to move its field of view 42 to capture thermal images of the tubes 12. The thermal imaging camera 38 produces surface temperature information 44 for each of the plurality of tubes. The surface temperature information 44 is provided to the computer model in the computer 34.

[0051] The surface temperature information 44 is used by the computer model in the computer 34 to calibrate the TDLAS temperature information 32. The TDLAS temperature information 32 is collected at least during continuous steady-state operation of the furnace. The thermal imaging camera surface temperature information 44 is collected periodically while the TDLAS temperature information 32 is being collected.

[0052] The computer model in the computer 34 provides optimised output parameters 46 for operation of the furnace. The optimised parameters from the model include the temperature profiles of the tubes as well as the flowrate, temperature, pressure, and composition of combustion gas, and furnace tube product gas. The optimised parameters provide output control instructions 48, that are used to adjust the input control instructions 20 for the burner control unit 18.