KR20030035855A - Method for self-correcting, dose control of liquid treatment chemicals - Google Patents

Abstract

PURPOSE: A method for controlling quantity of liquid treating compound used to process liquid in a liquid treating system for automatically correcting flow variables is provided. CONSTITUTION: The automatic correct quantitative control method of liquid treating compound comprises a step (a) of measuring an average moving liquid flux through treatment system, and producing liquid flux signals from measured values; a step (b) of measuring concentration of compound inside the treatment system, and producing compound concentration signals for measured values; a step (c) of transmitting the signals produced from the step (a) and signals produced from the step (b); a step (d) of automatically calculating input quantity of compound from the signals supplied to compound input controller(50); a step (e) of transmitting output signals from the compound input controller based on the input quantities calculated in the step (d) to compound supply system(60); a step (f) of discharging compound from the step (d) into inlet flow(20) by responding to output signals of the step (e); and a step (g) of continuously repeating the steps (a) to (f) during liquid treatment process.

Description

METHOD FOR SELF-CORRECTING, DOSE CONTROL OF LIQUID TREATMENT CHEMICALS}

Technical Field of the Invention

The present invention relates to a method for dose control of liquid treatment chemicals in a self-calibrating manner. More particularly, the present invention relates to a method for controlling the volume of liquid processing chemical used to process a liquid in a liquid processing system that self-corrects flow variables.

Prior art of the invention

Control of feed chemicals used in the processing of liquids in treatment systems such as wastewater filter systems can be automated through the use of computerized control devices. Problems can arise during automatic dosing of chemicals into the treatment system due to inaccurate measurement of chemicals present in the system and variable liquid to liquid ratios when the liquid flow rate is variable. Liquid flow rate may vary due to several factors:

1. a pump that increases and decreases influent through the system by opening and closing for a short time during the treatment process;

2. Additional pump added to the treatment system for the required time. For example, during storm surges an additional pump is needed to pump wastewater into the filter.

Even a short increase in the inflow stream causes a peak in the flow through the treatment system which can lead to inaccuracies in the input process.

In the past, input has been performed by laboratory or bench testing influent chemical concentrations and measuring influent flow. Subsequently, a dose calculation was performed and the input device, such as the chemical feed pump, was adjusted manually according to the above calculation. After a few years, partial pacing of the input pump was performed using the influent flow signal. However, there was still a need to manually test the incoming chemical concentration and manually fine tune the dosing rate of the pump. After a while, when the incoming chemical concentrations are reasonably stable, it has been found that process treatment plants, such as wastewater plants, have stringent effluent standards, eg meeting environmental approvals. Changing the dosing rate to maintain specific effluent chemical concentration test results is a more direct approach to guarantee better dosing results.

Recently, reliable automated analyzers for chemical concentrations have been made available and automation of the entire dosing process has become possible. Thus, the need for manual testing and manual adjustment is virtually eliminated. Further results indicate that the automated analyzer also performs a dosing process useful for other applications such as the addition of sodium or carbonate to the aerated biological reactor to control nitrification or the addition of iron or aluminum salts prior to the purifying agent to control phosphorus removal. It can be set up to detect some important chemicals in the process.

The accuracy of the method of measuring and measuring chemicals in both inflow and outflow flows of variable flow systems remains problematic due to inflow flow spikes. Improved adjustments for improved chemical dosing during water treatment are desirable.

It is an object of the present invention to provide a method for controlling the addition of liquid treatment chemicals by automatic dose control in a self-correcting manner.

1 is a schematic diagram of a method for automatic dose control of a liquid treatment chemical in a self-correcting manner in accordance with the present invention.

Summary of the Invention

Advantageously, the Applicant's innovative method results in self-calibrating, automatic dose control using enhanced control to improve chemical input during liquid treatment processes such as water treatment or wastewater filtration processes. Peaks or spikes in the flowmeter readings can cause inaccurate results during computer calculations of the chemical capacity to be added to the system. Since the method of the present invention uses a moving average of the liquid flow rate, it is self-correcting so that peaks or spikes at the flow rate are accounted for in the capacity control signal.

The method of adjusting the addition of treatment chemicals uses a self-calibrating, automated dose control system that includes mixing of signals from liquid flow meters, influent chemical concentration analyzers and / or effluent chemical concentration analyzers. This new blend provides the accuracy and control needed for improved chemical dosing. This signal is sent to a computerized chemical dose controller that controls the chemical input pump.

Liquids to be treated in a chemical system may include wastewater treated with chemicals as a carbon source. Carbon sources are often added to the denitrification reactor to promote denitrification.

In one method for automatic capacity control of water treatment chemicals in a self-calibrating manner, the flow meter is an inflow flow meter and the chemical concentration analyzer is an outflow analyzer or a mixture of inflow and outflow concentration analyzers. The mixing of liquid flow data and chemical concentration analysis is the criterion for controlling the input to improve the chemical input during water treatment.

The method for automatic dose control of the liquid treatment chemical in a self-calibrating manner during the liquid treatment process in a treatment system with an inflow stream and an outflow stream includes the following steps:

a. Measuring a moving average liquid flow rate through the processing system and generating a liquid flow signal from the measurement;

b. Measuring the concentration of the chemical in the treatment system and generating a chemical concentration signal from the measurement;

c. Transmitting the signal generated from step (a) and the signal generated from step (b) to a chemical input controller;

d. Automatically calculating a dose of a chemical from a signal supplied to the chemical input controller;

e. Transmitting an output signal from the chemical input controller based on the input calculated in step (d) to the chemical supply system;

f. Releasing the chemical from step (d) into the inlet stream in response to the output signal of step (e); And

g. Continuously repeating steps (a) to (f) during the liquid treatment process.

The moving average liquid flow of step (a) can be calculated by measuring the flow rate two or more times over a period of time and computing the average of the measurements. In this method, the liquid flow rate is measured at the inflow of the system. In addition, the liquid flow rate can be measured at the outflow of the system. The liquid flow rate can be adjusted by a flow pace multiplier. The concentration of chemical in step (b) can be measured in the inflow stream of the system. In addition, the concentration of chemicals in step (b) can be measured in the effluent flow of the system. In another alternative, the concentration of chemical in step (b) is measured in both the effluent stream and the inflow stream of the system. In one aspect of the invention, the chemical of step (b) is the same chemical as the chemical of step (d). Alternatively, the chemical of step (b) is a chemical that is different from the chemical of step (d).

Preferably, the measurement of the moving average liquid flow rate in step (a) and the measurement of the concentration of chemical in step (b) are carried out continuously. In addition, the measurement of the liquid flow rate in step (a) is continuous and the average of the measurements is taken within a certain period of time. The period for computing the average is 15 seconds to 30 minutes. The determination of the concentration of the chemical in step (b) is performed at intervals in the range of one minute to about 15 minutes.

In one embodiment, the liquid of the liquid treatment process is water and the treatment process is a water treatment process.

The self-calibrating method of self-calibration can be used in denitrification systems with inflow and outflow streams, where the chemical to be adjusted is nitrate-nitrogen during the water treatment process and the chemical source of organic carbon is the feed chemical. The method includes the following steps:

a. Measuring a moving average water flow rate through the treatment system and generating a water flow signal from the measurement;

b. Measuring the concentration of nitrate-nitrogen in the inlet stream of the treatment system and generating a chemical concentration signal from the measurement;

c. Transmitting the signal generated from step (a) and the signal generated from step (b) to a chemical input controller;

d. Automatically adjusting the nitrate / nitrogen signal by one or more adjustable dose factors;

e. Automatically calculating a dose of feed chemical from the adjusted signal supplied to the chemical input controller;

f. Transmitting an output signal from the chemical input controller based on the input calculated in step (e) to the chemical supply system;

g. Releasing the feed chemical into the inlet stream in response to the output signal of step (f); And

h. Continuously repeating steps (a) to (g) during the denitrification process.

In the process, the feed chemical is selected from the group consisting of alcohols and volatile fatty acids. Preferably, the feed chemical is methanol. In one aspect, the water flow rate signal of step (c) is automatically adjusted by the flow face multiplier. In another aspect, the concentration of nitrate-nitrogen is measured in both the outflow and inflow streams of the system. Preferably, a setpoint for effluent nitrate-nitrogen is selected and an effluent flow concentration signal is generated from the measurement of the concentration of nitrate-nitrogen in the effluent stream and the concentration signal is sent to a chemical dosing controller.

In one embodiment, the difference between the nitrate-nitrogen effluent concentration and the target value is calculated to produce a control response, where the control response is adjusted by one or more susceptibility factors and the adjusted control response changes the input of feed chemical. It is automatically incorporated into the calculation. Preferably, the dosage is used to generate a modified output signal that is sent from the chemical dosing controller to the chemical supply system. In addition, the modified output signal from the chemical dosing controller is sent to the chemical supply system after a reset time. In one embodiment of the invention, the reset time is entered manually. In addition, the reset time is a variable that is automatically calculated based on the hydraulic dwell time. Hydraulic residence time is calculated by reading the volume level indicator in the treatment tank and dividing the volume by the moving average flow rate. Reset time is based on hydraulic residence time and process reaction time during the process. The nitrate-nitrogen signal is automatically adjusted by one or more adjustable dose factors.

In an alternative method for the automatic capacity control of nitrate-nitrogen in a self-correcting manner during a water treatment process in a nitriding treatment system using a chemical source of organic carbon as feed chemical with an inflow stream and an outflow stream, the method comprises It includes the following steps:

a. Selecting a target value for effluent nitrate-nitrogen;

b. Measuring a moving average water flow rate through the treatment system and generating a water flow signal from the measurement;

c. Measuring the concentration of nitrate-nitrogen in the effluent stream and generating a chemical concentration signal from the measurement;

d. Transmitting the signal generated from step (b) and the signal generated from step (c) to a chemical input controller;

e. Calculating a difference between the nitrate-nitrogen effluent concentration and a target value to generate a control response;

f. Adjusting the control response by one or more susceptibility factors;

g. Automatically calculating the dose of feed chemical from the control response;

h. Transmitting an output signal from the chemical input controller based on the input calculated in step (g) to the chemical supply system;

i. Releasing the feed chemical into the inlet stream in response to the output signal of step (h); And

j. Continuously repeating steps (a) to (i) during the denitrification process.

Nitrate-nitrogen concentrations are measured in both the inlet and outlet streams. In one aspect, the concentration of nitrate-nitrogen in the inflow stream is measured and an inflow stream concentration signal is generated and sent to the chemical dosing controller. Preferably, the inflow flow concentration signal is adjusted by a volume factor which can be adjusted and the water flow rate signal from step (d) is adjusted by a flow phase multiplier.

In a preferred embodiment, the calculation of the output signal from the chemical input controller to the chemical supply system is based on the average water flow rate, the concentration of nitrate-nitrogen in the inlet stream and the concentration of nitrate-nitrogen in the effluent stream. Preferably, the calculation of the subsequent control response in step (e) is performed after the reset time. The reset time may be entered manually or, alternatively, the reset time may be an automatically calculated variable based on the hydraulic residence time and the process reaction time during the process.

The derived control response is preferably generated to neutralize the rapid rate of change that causes the target value to approach or move away from it. Preferred derived control responses are generated by measuring the first outlet concentration before the reset time, measuring the second outlet concentration at the reset time, comparing the first outlet concentration with the second outlet concentration and adjusting the control response accordingly. .

In an alternative embodiment of the method for automatic dose control of liquid treatment chemicals during a treatment process in a liquid treatment system using feed chemicals having an inflow stream and an outflow stream, the method comprises the following steps:

a. Selecting a target value for the chemical in the effluent stream;

b. Measuring a liquid flow rate through the processing system and generating a liquid flow signal from the measurement;

c. Measuring the concentration of the chemical of step (a) in the inflow stream and generating an influent chemical concentration signal from the measurement;

d. Measuring the concentration of the chemical of step (a) in the effluent stream and generating an effluent chemical concentration signal from the measurement;

e. Transmitting the signal generated from step (b) to a chemical dosing controller and generating a primary control response;

f. Adjusting the primary control response by the flow phase multiplier;

g. Transmitting the signal generated from step (c) to the chemical dosing controller and generating a secondary control response;

h. Adjusting the secondary control response by a dose factor that can be adjusted;

i. Transmitting the signal from step (d) to the chemical dosing controller and calculating the difference between the effluent chemical concentration and the target value to generate a tertiary control response;

j. Adjusting the tertiary control response by one or more susceptibility factors;

k. Continuously calculating the dose of feed chemical from the primary control response and the secondary control response while incorporating the tertiary control response from step (f) after the reset period;

l. Sending an output signal from the chemical input controller based on the input calculated in step (k) to the chemical supply system;

m. Releasing the feed chemical into the inlet stream in response to the output signal of step (l); And

n. Continuously repeating steps (a) to (m) during the treatment process.

Preferably the chemical of step (a) is the same chemical as the chemical of step (m). In one aspect, the chemical of step (a) is a chemical that is different from the chemical of step (m) (38). In one embodiment, the reset time is entered manually. In addition, the reset time is an automatically calculated variable based on the hydraulic residence time and the process reaction. Hydraulic residence time is calculated by reading the volume level indicator in the treatment tank and dividing the volume by the moving average flow rate. Process reaction time is the time taken for the treatment process to respond to the presence of injected chemicals. Reset time is based on hydraulic residence time and process reaction time during the process.

Detailed description of the invention

In a new and improved method of controlling the addition of liquid treatment chemicals by automatic dose adjustment with self-calibration, the calculation of the amount of chemical to be introduced into the system includes the signal from the liquid flow meter, the signal from the incoming chemical concentration analyzer, and And / or mixing the moving average of the signal from the effluent chemical concentration analyzer. This method of automatic dose control of chemicals is useful for any system that treats liquids by the addition of chemicals, such as water treatment systems or wastewater treatment systems. These signals from the chemical concentration analyzer are sent to a computerized chemical dose controller that analyzes and adjusts the data from the signal and generates an output signal that controls the chemical dosing device so that the appropriate amount of chemical is added to the treatment tank or filter. Is added to.

The method of the present invention performs self-calibrating automatic dose control using enhanced control to improve chemical dosing during the treatment process. Peaks or spikes at the flow rate can occur by adding more pumps to the treatment system during storm surges or other increased inflow flows. Peaks or spikes may also be caused by pumps that open and close during the water treatment process. Peaks or spikes in the flowmeter readings can cause inaccurate results during computer calculations of the chemical capacity to be added to the system. The method of the present invention uses a moving average of the liquid flow rate to self-correct so that peaks or spikes at the flow rate are accounted for in the capacity control signal.

Advantageously, the automatic dose control method also has the ability to set the maximum positive and negative limits of the control action, improve the input of chemicals during water treatment by allowing previous changes to be disseminated through the system and displayed on the outflow sensor. It includes.

Liquid treatment systems using automatic dose control include the denitrification of wastewater treatment systems, the addition of sodium carbonate or sodium bicarbonate for biological aeration and the addition of alum or iron salts in a process designed to remove phosphates.

Referring to the schematic diagram of FIG. 1, a liquid or wastewater treatment system using a chemical process in the treatment of wastewater is signaled to the process inlet stream 20, and to the outlet stream 30, a variable dose of chemical input or supply system 60. And a chemical supply pump 60 for injecting the appropriate chemicals into the computerized control system, such as the treatment system, referred to as the chemical dosing controller 50 to produce the chemicals. Preferably, chemical feed pump 60 includes an automatically variable output through a change in pump speed and / or a change in pump stroke length. The pump may be coupled to a signal from chemical input controller 50 based on two or three variables, input of process moving average water flow, input of incoming chemical concentration, and alternatively input of outflow chemical concentration. Is activated by

The process water flow rate, which is the first variable, is measured by the electromagnetic flowmeter 25. The flow meter may preferably be located in the inflow stream 20, or alternatively in the outflow stream 30. Flowmeter 25 measures the water flow rate through treatment system 10. The average of the flow rates is calculated by measuring the water flow rate two or more times over a period of time and computing the average of the measurements over that period. For example, the flow rate can be measured every 15 seconds for 3 minutes and the average of these measurements can provide a moving average flow rate. In this way, exceptional measurements caused by peaks or spikes in the flow rate are corrected. The water flow signal is generated from the average of the measurements. If a flow meter is present in the effluent flow, the readout will be delayed due to delays in process plant piping and tank capacity. This time delay can be accounted for in the chemical input controller 50 by the system operator.

Preferably, the controller 50 generates a primary control response based on the water flow signal. The controller 50 adjusts the primary control response from the inflow or outflow flowmeter by the flow face multiplier. Any adjustment of this adjustment or control response can be performed manually by the operator, but automatic adjustment pre-programmed into the controller 50 is preferred. The adjusted primary control response or process flow factor may be sent to the chemical supply system as an input signal. These measurements and signals are continually generated as often as about 0.5 seconds below about 5 minutes. In addition, the adjusted primary control response may be mixed with the secondary and / or tertiary control response to generate an input signal. The maximum output of the chemical supply system 60 depends on the water flow rate through the water treatment system 10. The calculation of the primary control response is expressed as follows:

Primary Control Response = Flow Face Multiplier × Average Flow ÷ Flow Meter Maximum Range

The concentration of chemicals in the inflow stream is the second parameter in determining chemical inputs. Chemical analyzer 28 is used to measure the chemical concentration in the influent stream and generate a signal sent to chemical input controller 50. Chemical analyzers for measuring chemical concentrations are well known in the art and will not be described further herein. Chemical input controller 50 generates a secondary control response based on the chemical signal from the chemical. The secondary control response is adjusted by the capacity factor, which can be adjusted. The input factors that can be adjusted are determined by the operator to allow for differences in process efficiency. Standard dose factors known in the art may be used to adjust the secondary control response. The standard dose factor is the empirical or generally required ratio between the chemical added and the chemical it responds to; Standard factors are known in the art. If methanol is used to remove nitrate-nitrogen, the standard dose factor is about 3.0.

The calculation of the secondary control response is expressed as follows:

Secondary control response = (volume factor adjustable × measured inlet concentration) ÷ (standard dose factor × maximum inlet concentration)

The output or input signal from chemical input controller 50 to feed pump 60 is then corrected by the adjusted secondary control response. The calculation of the input signal at this stage of the automatic dose control method is expressed as follows:

Input signal = adjusted primary control response × adjusted secondary response

Measurement of the incoming chemical concentration and generation of signals for the adjusted primary and secondary control responses can occur at intervals of less than 1 second to about 15 minutes.

The third parameter in calculating the chemical input includes the effluent stream chemical concentration. The measurement of the effluent flow chemical concentrations and the transmission of signals based on these measurements to the chemical dosing controller 50 generates a tertiary control response. Mixing these variables with the primary control response or the secondary control response or both is desirable to adjust to change the level of process efficiency or to control to ensure a specific effluent chemical concentration result for the target value. The effluent chemical concentration is measured by the effluent concentration analyzer 38 which generates a signal that is sent to the chemical input controller 50. Chemical input controller 50 generates a tertiary control response based on the chemical signal from chemical analyzer 38. The tertiary control response is based on the effluent concentration. Tertiary control response is a more complex calculation. The tertiary control response controls for the selected effluent concentration target value.

An important feature of the control method of the present invention is that between controlling the change in chemical input upstream of the process and waiting for the result to be replenished through the pipe and tank capacity to the point where the process responds and the effluent concentration results are measured. It considers the possibility of elapsed time and delay time. The most useful controllers on the market are designed to work continuously, which reveals control problems when there is a delay.

In the method of the present invention, the control system continuously operates using the adjusted primary and secondary control responses described above to generate a chemical input signal, generating a tertiary control response at discrete intervals. This interval is known as the reset time. The reset time can be set manually or automatically at specific and constant intervals. If the reset time is calculated automatically, the next reset interval can be adjusted based on the current process flow rate, the known volume of pipe and tank capacity between the control point and the measuring point, and experience during the process itself in response to control changes. Based on a period of time (process reaction time). The calculation of the secondary control response is based on the hydraulic residence time and the process reaction time during the process. Hydraulic residence time is calculated by reading the volume level indicator in the treatment tank and dividing the volume by the moving average flow rate. The reset time is an automatically calculated variable based on the hydraulic residence time and the process reaction time during the process. The reset time can be represented by the following equation:

Reset time = (process tank volume volume ÷ moving average flow rate) + process reaction time

If this interval is stopped, the runoff concentration factor is recalculated and the tertiary control response is mixed with the primary and secondary control responses to produce a chemical input output signal. Preferably, after the reset time, the adjusted tertiary control response is incorporated into the calculation and the dosage of feed chemicals based on the adjusted primary control and adjusted secondary control response is calculated and transmitted continuously. Measurement of the incoming chemical concentration and generation of signals for the adjusted primary and secondary responses can occur at intervals in the range of less than 1 second to about 15 minutes. The time between reset intervals is from about 5 minutes to about 120 minutes, or even as long as 3 to 4 hours in very large processing systems. In one preferred method, the reset time is from about 30 minutes to about 60 minutes. After the reset time expires, the new reset interval is calculated using the process flow at that time and the cycle starts again.

The tertiary control response is based on the effluent chemical concentration. When tertiary control is initiated for the first time, it starts with a neutral factor, such as work (1), which neither decreases nor increases the existing control response. The change in tertiary control response is calculated by comparing the measured effluent concentration against a target value established and used by the plant operator as control. Changes to the tertiary control response are known in the art as "step changes". The target value is entered into the chemical dosing controller and used to calculate the tertiary control response. This calculation is performed when the above-described reset period has passed. The target value is subtracted from the runoff concentration to determine the "error" and multiplied by the sensitivity factor. Susceptibility factors are selected by the operator based on the operator's experience with the particular liquid treatment process requiring input. Susceptibility factors can have two values. One of the sensitivity factor values is designed for use when the runoff concentration exceeds the target value. The other is used when the effluent concentration is below the target value.

The phase change equation can be expressed as follows:

Phase Change = Susceptibility Factor × (Outflow Concentration-Target Value)

100

The step change calculation is positive if the effluent concentration exceeds the target value, which increases the magnitude of the tertiary control response and accelerates the chemical supply system, preferably the input pump 60, during the next reset period. The step change is negative if the effluent concentration is below the target value, which reduces the tertiary control response and reduces the dose.

When the adjusted tertiary control response is calculated, the adjusted tertiary control response can be incorporated into the equation used to calculate the input output signal after the reset period. If this applies to the input signal equation, the complete equation containing the cubic control response is expressed as follows:

Input signal = adjusted primary control response × adjusted secondary response × adjusted third control response

After the dosing signal is automatically calculated by the chemical dosing controller 50, the signal is sent to the chemical supply system 60 or pump to input the indicated amount of feed chemical to the treatment system. The feed chemical is preferably introduced into inlet stream 20.

In the practice of the method, the process variable may approach or move away from the target value at high speed just before the next tertiary control response is calculated. Rather than the next step change in chemical dosing based solely on the final runoff concentration under these conditions, this helps to modify the next tertiary control response that reverses the rate of change algae and induces a modified tertiary control response. Is referred to as a control response. In the practice of the method of the invention, the derived control response is generated by measuring the effluent concentration at a time that can be adjusted before the reset period ends and comparing it with the effluent concentration at the end of the reset period. If the rate of change in the effluent concentration is rapid, the change in the next chemical input is either raised or lowered accordingly. The rate of change and the response factor will vary with each installation. The factor used will also depend on whether the runoff concentration is above or below the target value at the end of the reset.

Example: The effluent concentration (EC) was examined 15 minutes before the reset (R) and then also on R. A 0.3 mg / L change in either direction was assumed to be a rapid rate of change for this process. The calculated step change by 25% factor is increased or decreased to counteract the direction of change. Representative equations are as follows:

When EC _R > SP and EC _R -EC _R-15 > 0.3, SC _NEW = 1.25 x SC _CALC

For EC _R -EC _R-15 ≤ -0.3 SC _NEW = 0.75 x SC _CALC and

When EC _R <SP and EC _R -EC _R-15 > 0.3, SC _NEW = 0.75 x SC _CALC

For EC _R -EC _R-15 ≤ -0.3, SC _NEW = 1.25 x SC _CALC

Where EC is the effluent chemical concentration, R is the reset, SP is the target value, and SC is the step change as calculated according to the equation described above. Factor, 1.25, represents a 25% increase and factor 0.75, represents a 25% decrease. These factors are adjusted by the operator based on experience in using a particular liquid treatment process.

When tertiary control is initiated, the tertiary control response is based on the runoff concentration factor (ECF) and starts at 1.0. At the end of the reset time, a step change calculation is made and the result is added to the current runoff concentration factor. This is repeated at the end of each reset period:

ECF _NEW = ECF _NOW + SC _NEW

During the implementation of the method, the steps keep the control input and output within a reasonable range. In order to exclude the tertiary control response from out of control, an upper and lower limits for the tertiary control action that the operator can adjust are programmed into the chemical dosing controller. The runoff concentration will not allow to exceed this limit. During one preferred method, the minimum and maximum allowable signals for the input pump can be set. Since the reset time can be set manually or automatically, the minimum and maximum reset time limits can be set for each.

Preferably, the control system may allow for manual control, flow control, flow and inlet concentrations, flow and outlet concentrations, or flow and inlet and outlet concentrations. This allows for maintenance on different parts of the system as well as different device arrangements. The list of some of the possible control variables used during the practice of the present invention is as follows:

Control variables

External setting (MMI) Internal setting (PLC) Adjustable Volume Factor Flow Face Multiplier Process Tank Capacity Volume Target Value (SP) Process Response Time Susceptibility Factor + Fast Change Rate Above SP-Fast Change Rate Above SP + Fast Change Rate Below SP-Fast Change Rate Below SP Rate of change factor approaching to SP Factor of change away from SP Minimum ECF Maximum ECF Maximum ECF Maximum Input Signal Minimum Input Signal Reset Time Automatic / Manual Mode Manual Reset Time Manual Input Signal Automatic / Manual Control Mode Flow Control Mode Flow + Influent Concentration Control Mode Flow + Outflow Concentration Control Mode Flow + Inflow + Outflow Concentration Control Mode Standard Dose Factor Maximum Inlet Concentration Flowmeter Range Maximum Reset Time Above Maximum Susceptibility Factor Above SP Maximum Susceptibility Factor Below SP Reset Time

In one preferred method of the present invention, the liquid treatment system described will be a wastewater treatment system, and the process will be a denitrification process using a source of organic carbon as the chemical introduced into the wastewater stream. However, the method of the present invention can be applied to any liquid treatment system that requires automatic dosing of treatment chemicals, such as the system described above, and is not limited to wastewater treatment systems.

Denitrification is the biochemical conversion of aqueous nitrate-nitrogen and nitrite-nitrogen into nitrogen gas. Denitrification reactors can assume many forms including upflow or downflow granular filters or packaged beds, as well as stirred tanks or rotating biological shrinkers. Chemical sources of organic carbon are used in the denitrification process. The carbon source is typically an organic acid such as an alcohol or volatile fatty acid. One preferred alcohol is methanol, and alternatively acetic acid can be a chemical source. Preferably, the wastewater treatment system comprises an inflow stream 20 and an outflow stream 30. In the denitrification process, the input of feed chemicals, such as methanol, is calculated from the nitrate-nitrogen concentration in the wastewater stream. The concentration of nitrate-nitrogen can be calculated in the inflow stream 20 or the outflow stream 30 or both. During the implementation of the method in the denitrification process, a moving average water flow rate is measured through the treatment system. The average of the flow rates is calculated by measuring the water flow rate two or more times over a period of time and computing the average of the measurements over this period. A signal based on the average flow rate is generated and sent to the chemical input controller 50 as the primary control response. The primary control response can be adjusted by the flow face multiplier. The nitrate-nitrogen concentration is then measured in the inflow stream 20 and a signal is generated and sent to the chemical input controller 50 as a secondary control response. The secondary control response can be automatically corrected by one or more adjustable dose factors. By using a standard dose factor and another operator adjustable dose factor, the operator can modify the secondary control response based on his experience in using the liquid handling system to be injected. In one embodiment of the invention, the adjusted primary control response and the adjusted secondary control response are mixed to generate a chemical input output signal that is sent from the chemical input controller 50 to the chemical supply system 60. . Chemical supply system 60 supplies methanol in an amount based on the chemical input output signal.

In addition, nitrate-nitrogen concentrations can be measured in the effluent stream 30. The tertiary control response based on the effluent concentration is calculated by comparing the measured effluent concentration with a target value established and used by the plant operator as control. The target value is entered into the chemical dosing controller and used to calculate the tertiary control response. This calculation is performed when the reset period described above has passed. The target value is subtracted from the effluent concentration to measure the "error" and multiplied by the susceptibility factor to produce an adjusted tertiary control response. When the adjusted tertiary control response is calculated, the adjusted tertiary control response can be incorporated into the equation used to calculate the input output signal after the reset period has expired. If this applies to the input signal equation, the complete equation containing the cubic control response is expressed as follows:

Input signal = adjusted primary control response × adjusted secondary response × adjusted tertiary control response

The input signal is then sent to the chemical supply system 60 to supply the required amount of methanol into the inlet stream 20.

Attempts of the self-correcting chemical input control system of the present invention have shown a reduced tendency for oversupply or undersupply of treatment chemicals and stabilized effluent chemical concentrations. The improved method (1) operates the treatment system to a greater degree of conversion or lower effluent chemical concentration than was possible before the present invention, without the risk of overfeeding the treatment chemical, and (2) still reliably effluent While meeting target or environmental approvals, it has been possible to use a lower treatment chemical to operate the treatment system at a lower degree of conversion or at a higher effluent chemical concentration.

The foregoing description is an illustration and description of preferred embodiments of the invention, and variations in size, shape, material, and other details will be apparent to those skilled in the art. It is intended that all such changes and modifications fall within the spirit or scope of the appended claims.

As described above, the present invention provides a self-correcting chemical dosing control system to achieve a reduced tendency for oversupply or undersupply of treatment chemicals and a stabilized effluent chemical concentration in a liquid treatment system.

Claims (39)

a. Measuring a moving average liquid flow rate through the processing system and generating a liquid flow signal from the measurement; b. Measuring the concentration of the chemical in the treatment system and generating a chemical concentration signal from the measurement; c. Transmitting the signal generated from step (a) and the signal generated from step (b) to a chemical input controller; d. Automatically calculating a dose of a chemical from a signal supplied to the chemical input controller; e. Sending an output signal from the chemical input controller based on the input calculated in step (d) to the chemical supply system; f. Releasing the chemical from step (d) into the inlet stream in response to the output signal of step (e); And g. Continuously repeating steps (a) to (f) during the liquid treatment process to automatically self-calibrate the liquid treatment chemicals during the liquid treatment process in a treatment system having an inflow and an outflow. Way. The method of claim 1, wherein the moving average liquid flow rate is calculated by measuring the flow rate two or more times over a period of time and computing the average of the measurements. The method of claim 1 wherein the flow rate is measured at the inflow of the system. The method of claim 1 wherein the flow rate is measured at the outflow of the system. The method of claim 1 wherein the flow rate is adjusted by a flow pace multiplier. The method of claim 1, wherein the concentration of chemical in step (b) is measured in the inflow stream of the system. The method of claim 1, wherein the concentration of chemical in step (b) is measured in the effluent flow of the system. The method of claim 1, wherein the concentration of chemical in step (b) is measured in both the effluent stream and the inflow stream of the system. The method of claim 1 wherein the chemical of step (b) is the same chemical as the chemical of step (d). The method of claim 1 wherein the chemical of step (b) is a different chemical from the chemical of step (d). The method of claim 1, wherein the measurement of the liquid flow rate in step (a) and the measurement of the concentration of chemicals in step (b) are carried out continuously. The method of claim 1, wherein the measurement of the liquid flow rate in step (a) is continuous, the average of the flow rates is calculated after a set time, and the measurement of the concentration of chemicals in step (b) is carried out at one to about 15 minute intervals. Method performed at intervals within the range. The method of claim 1 wherein the liquid in the liquid treatment process is water and the treatment process is a water treatment process. a. Measuring a moving average water flow rate through the treatment system and generating a water flow signal from the measurement; b. Measuring the concentration of nitrate-nitrogen in the inlet stream of the treatment system and generating a chemical concentration signal from the measurement; c. Transmitting the signal generated from step (a) and the signal generated from step (b) to a chemical input controller; d. Automatically adjusting the nitrate / nitrogen signal by one or more adjustable dose factors; e. Automatically calculating a dose of feed chemical from the adjusted signal supplied to the chemical input controller; f. Transmitting an output signal from the chemical input controller based on the input calculated in step (e) to the chemical supply system; g. Releasing the feed chemical into the inlet stream in response to the output signal of step (f); And h. Treatment of water in a denitrification system using a chemical source of organic carbon as feed chemical, with continuous inflow and outflow, including repeating steps (a) to (g) during the denitrification process. Self-calibration control of nitrate-nitrogen during the process. 15. The method of claim 14, wherein the feed chemical is selected from the group consisting of alcohols and volatile fatty acids. 15. The method of claim 14, wherein the feed chemical is methanol. 15. The method of claim 14, wherein the water flow rate signal of step (c) is automatically adjusted by a flow face multiplier. 15. The method of claim 14, wherein the concentration of nitrate-nitrogen is measured in both the effluent stream and the inflow stream of the system. 19. The method of claim 18, wherein a setpoint for effluent nitrate-nitrogen is selected, an effluent flow concentration signal is generated from the measurement of the concentration of nitrate-nitrogen in the effluent stream, and the concentration signal is sent to a chemical dosing controller. How to feature. 19. The method of claim 18, wherein the difference between the nitrate-nitrogen effluent concentration and the target value is calculated to produce a control response, the control response is adjusted by one or more susceptibility factors, and the adjusted control response is input to the feed chemical. Automatically incorporated into the calculation for. 21. The method of claim 20, wherein the input is used to generate a modified output signal that is sent from the chemical input controller to the chemical supply system. 21. The method of claim 20, wherein the modified output signal from the chemical dosing controller is sent after a reset time to the chemical supply system. 23. The method of claim 22, wherein the hydraulic residence time is calculated by reading the volume level indicator in the treatment tank and dividing the volume by a moving average water flow rate. 24. The method of claim 23, wherein the reset time is an automatically calculated variable based on the hydraulic residence time and process reaction time during the process. 15. The method of claim 14, wherein the nitrate-nitrogen signal is automatically adjusted by one or more adjustable dose factors. a. Selecting a target value for effluent nitrate-nitrogen; b. Measuring a moving average water flow rate through the treatment system and generating a water flow signal from the measurement; c. Measuring the concentration of nitrate-nitrogen in the effluent stream and generating a chemical concentration signal from the measurement; d. Transmitting the signal generated from step (b) and the signal generated from step (c) to a chemical input controller; e. Calculating a difference between the nitrate-nitrogen effluent concentration and a target value to generate a control response; f. Adjusting the control response by one or more susceptibility factors; g. Automatically calculating the dose of feed chemical from the control response; h. Sending an output signal from the chemical input controller based on the input calculated in step (g) to the chemical supply system; i. Releasing the feed chemical into the inlet stream in response to the output signal of step (h); And j. A water treatment process in a denitrification system using a chemical source of organic carbon as feed chemical, having an inflow stream and an outflow stream, including continuously repeating steps (a) to (i) during the denitrification process. Automatic dose control of nitrate-nitrogen in a self-calibrating manner. 27. The method of claim 26, wherein the concentration of nitrate-nitrogen is measured in both the inlet and outlet streams. 27. The method of claim 26, wherein the concentration of nitrate-nitrogen in the influent stream is measured and an influent stream concentration signal is generated and sent to the chemical input controller. 29. The method of claim 28, wherein the inflow flow concentration signal is adjusted by a volume factor that can be adjusted and the water flow rate signal from step (d) is adjusted by a flow face multiplier. 29. The method of claim 28, wherein the calculation of the output signal from the chemical dosing controller sent to the chemical supply system is based on a moving average water flow rate, the concentration of nitrate-nitrogen in the inlet stream and the concentration of nitrate-nitrogen in the effluent stream. Characterized in that. 27. The method of claim 26, wherein the calculation of the subsequent control response in step (e) is performed after a reset time. 32. The method of claim 31, wherein the hydraulic residence time is calculated by reading the volume level indicator in the treatment tank and dividing the volume by a moving average water flow rate. 33. The method of claim 32, wherein the reset time is an automatically calculated variable based on the hydraulic residence time during the process and the process reaction time. 32. The method of claim 31, wherein the derived control response is generated to neutralize a rapid rate of change that causes the target value to approach or move away from the target value. 35. The method of claim 34, wherein the induced control response measures the first outflow concentration before the reset time, measures the second outflow concentration at the reset time, compares the first outflow concentration with the second outflow concentration, and accordingly controls Generated by adjusting the response. a. Selecting a target value for the chemical in the effluent stream; b. Measuring a moving average liquid flow rate through the processing system and generating a liquid flow signal from the measurement; c. Measuring the concentration of the chemical of step (a) in the inflow stream and generating an influent chemical concentration signal from the measurement; d. Measuring the concentration of the chemical of step (a) in the effluent stream and generating an effluent chemical concentration signal from the measurement; e. Transmitting the signal generated from step (b) to a chemical dosing controller to generate a primary control response; f. Adjusting the primary control response by a flow pace modifier; g. Transmitting the signal generated from step (c) to a chemical dosing controller to generate a secondary control response; h. Adjusting the secondary control response by a dose factor that can be adjusted; i. Transmitting the signal from step (d) to the chemical dosing controller and calculating the difference between the effluent chemical concentration and the target value to generate a tertiary control response; j. Adjusting the tertiary control response by one or more susceptibility factors; k. Calculating the hydraulic retention time during the process by reading the volume level indicator in the treatment tank and dividing the volume by the moving average water flow rate; l. Automatically calculating the reset time based on the hydraulic residence time and the process reaction time; m. Continuously calculating the dose of feed chemical from the primary control response and the secondary control response while incorporating the tertiary control response from step (f) after the reset time; n. Transmitting an output signal from the chemical input controller based on the input calculated in step (m) to the chemical supply system; o. Releasing the feed chemical into the inlet stream in response to the output signal of step (n); And p. Self-calibrating the liquid treatment chemicals during the treatment process in a liquid treatment system using feed chemicals, comprising continuously repeating steps (a) to (o) during the treatment process. How to do automatic dose control in a way. 37. The method of claim 36, wherein the chemical of step (a) is the same chemical as the chemical of step (o). 37. The method of claim 36, wherein the chemical of step (a) is a different chemical from the chemical of step (o). 37. The method of claim 36, wherein the reset time is entered manually.