Computerized chemical injection system for hydrogen sulfide control in a waste water stream

• US 5,454,918 A
• Filed: 10/05/1994
• Issued: 10/03/1995
• Est. Priority Date: 08/12/1991
• Status: Expired due to Fees

• Current Assignee: Clearwater Industries Incorporated
• Original Assignee: Clearwater Industries Incorporated
• Inventors: Jones, Randy L., Javadi, Younes, Werner, Douglas F.
• Primary Examiner(s): Niebling, John
• Assistant Examiner(s): BELL, BRUCE F
• Application Number:
  US08/318,265
• Time in Patent Office: 363 Days
• Field of Search: 204/153.19, 204/153.1
• US Class Current: 205/786.5
• CPC Class Codes: B01D 53/1493 Selection of liquid materials for use as absorbents
• CPC Class Codes: B01D 53/30 Controlling by gas-analysis apparatus regulating non electrical variables in general G05D
• CPC Class Codes: C02F 1/008 Control or steering systems not provided for elsewhere in subclass C02F
• CPC Class Codes: G01N 33/0044 Sulphides, e.g. H2S
• CPC Class Codes: G01N 33/182 Specific anions in water
• CPC Class Codes: G05D 21/02 characterised by the use of electric means
• CPC Class Codes: Y10S 210/916 Odor, e.g. including control or abatement
• CPC Class Codes: Y10T 436/184 Only hydrogen sulfide

Abstract

A system for continuously monitoring the hydrogen sulfide concentration present in the atmosphere above a waste water stream, such as a sewerage stream, and for controlling the amount and time of injecting a specified chemical into the waste water stream in order to control the quantity of hydrogen sulfide which would evaporate into the atmosphere. This system comprises the steps of obtaining a sample of atmosphere above the stream; routing the sample of air through a sensor for determining the concentration of hydrogen sulfide gas within the quantity of air determining the amount of an amine-based dopant to add to the waste water; sending a signal from the controller to a chemical injection pump for injecting the determined quantity of chemical compound into the waste water stream to absorb some of the hydrogen sulfide gas; continually monitoring the stream for determining the concentration of hydrogen sulfide gas in the stream following the introduction of chemical compound thereunto; and adding additional compound on a continuing basis, as needed, depending on the concentration of hydrogen sulfide within the stream.

Claims

1. A method for obtaining H₂ S concentration readings using an H₂ S sensor which provides a voltage output based on H₂ S concentration, the method comprising the steps of:

providing a zero H₂ S concentration gas to the sensor for a period of time to ensure a zero level environment and obtaining a zero voltage reading;

providing a set maximal H₂ S concentration gas to the sensor for a period to ensure a maximal level environment and obtaining a full scale voltage reading;

purging the sensor for a period to provide a substantially zero level environment;

providing a set concentration of H₂ S bearing gas to the sensor for a period of time to provide a set voltage change;

determining the slope of the concentration to voltage curve of the sensor for the set voltage change;

adjusting a stored concentration to voltage curve to conform with the zero and full scale voltage readings and the slope determination;

again purging the sensor to provide a substantially zero level environment;

monitoring the voltage change as said again purging step is occurring to provide a first clearing rate;

adjusting the stored concentration to voltage curve to conform with the first clearing rate;

providing the set concentration of H₂ S bearing gas to the sensor for the same period as required to provide said set voltage change;

determining the slope of concentration to voltage curve resulting from said providing for said same period step;

adjusting the stored concentration to voltage curve to conform with the slope determination determined based on the same period step;

yet again purging the sensor to provide a substantially zero level environment after the providing for the same period step;

monitoring the voltage change as the yet again purging is occurring to provide a second clearing rate;

adjusting the stored concentration to voltage curve to conform with the second clearing rate;

providing a sample gas to be measured to the sensor after adjusting the stored concentration to voltage curve to conform with the second clearing rate;

measuring the voltage of the sensor in the presence of the sample gas; and

linearizing the measured sample gas sensor voltage using the stored concentration to voltage curve and providing an H₂ S concentration reading.

2. The method of claim 1, further comprising the step of:

returning to the again purging step after providing said H₂ S concentration reading to obtain a next concentration reading.

3. The method of claim 2, wherein the loop from said again purging step to said linearizing step is performed every 2 to 3 minutes.

4. The method of claim 1, further comprising the steps of:

adjusting the gain of the sensor to increase output voltage after each step of adjusting the stored concentration to voltage curve to conform with the slope determination.