WO2020014228A1

WO2020014228A1 - On-line optimization and control of ammonia removal in distillation processes

Info

Publication number: WO2020014228A1
Application number: PCT/US2019/041009
Authority: WO
Inventors: Vincent Gerald SPAETH
Original assignee: Chemtreat, Inc.
Priority date: 2018-07-09
Filing date: 2019-07-09
Publication date: 2020-01-16

Abstract

An embodiment provides a method for measuring ammonia in waste water near a distillation column, including: obtaining an aqueous sample comprising waste water from a distillation column; measuring, using a nitrogen measurement device that performs oxidation of components of the aqueous sample, an amount of nitrogen in the obtained aqueous sample to provide real-time nitrogen measurement; identifying an amount of ammonia in the aqueous sample, wherein the identifying comprises correlating the measured amount of nitrogen to an amount of ammonia; and adjusting, based upon the identified amount of ammonia, a level of alkali injected into the distillation column and an amount of steam applied at the distillation column. Other embodiments are described and claimed.

Description

ON-LINE OPTIMIZATION AND CONTROL OF AMMONIA REMOVAL IN

DISTILLATION PROCESSES

CLAIM FOR PRIORITY

[0001] This application claims priority to U.S. Provisional Application No. 62/695,440 filed on July 9, 2018, entitled“ON-LINE OPTIMIZATION AND

CONTROL OF AMMONIA REMOVAL IN DISTILLATION PROCESSES”, which is incorporated by reference herein in its entirety.

BACKGROUND

[0002] Measurement of fluid characteristics can provide very useful information regarding the quality of the fluid or the fluid purification or refining process. Some of the purification or refining processes are used to make fluids safe for disposal. In other words, the purification or refining process may not make the fluid pure or clean, but, rather, may merely make the fluid safe for disposal using traditional fluid disposal techniques. For example, in the process of making coke, a by-product of steel-making, fluid that is used or created during the coke process is very hazardous. Thus, this waste water is sent through one or more distillation processes to remove the more harmful components from the waste water. After these distillation processes the resulting waste water is safer and can then be sent to a disposal area for disposal of the waste water using traditional techniques.

BRIEF SUMMARY

[0003] One embodiment provides a method for measuring ammonia in waste water near a distillation column, comprising: obtaining an aqueous sample comprising waste water from a distillation column; measuring, using a nitrogen measurement device that performs oxidation of components of the aqueous sample, an amount of nitrogen in the obtained aqueous sample to provide real-time nitrogen measurement; identifying an amount of ammonia in the aqueous sample, wherein the identifying comprises correlating the measured amount of nitrogen to an amount of ammonia; and adjusting, based upon the identified amount of ammonia, a level of alkali injected into the distillation column and an amount of steam applied at the distillation column.

[0004] A further embodiment provides a system for measuring ammonia in waste water near a distillation column, comprising: a nitrogen measurement device; a processor; and a memory device that stores instructions executable by the processor to: obtain an aqueous sample comprising waste water near a distillation column; measure, using the nitrogen measurement device that performs oxidation of components of the aqueous sample, an amount of nitrogen in the obtained aqueous sample to provide real-time nitrogen measurement; identify an amount of ammonia in the aqueous sample, wherein the identifying comprises correlating the measured amount of nitrogen to an amount of ammonia; and adjust, based upon the identified amount of ammonia, a level of alkali injected into the distillation column and an amount of steam applied at the distillation column.

[0005] The foregoing is a summary and thus may contain simplifications, generalizations, and omissions of detail; consequently, those skilled in the art will appreciate that the summary is illustrative only and is not intended to be in any way limiting.

[0006] For a better understanding of the embodiments, together with other and further features and advantages thereof, reference is made to the following description, taken in conjunction with the accompanying drawings. The scope of the invention will be pointed out in the appended claims.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0007] FIG. 1 illustrates an example method of measuring ammonia in waste water from a distillation column.

[0008] FIG. 2 illustrates an example of computer circuitry. DETAILED DESCRIPTION

[0009] It will be readily understood that the components of the embodiments, as generally described and illustrated in the figures herein, may be arranged and designed in a wide variety of different configurations in addition to the described example embodiments. Thus, the following more detailed description of the example

embodiments, as represented in the figures, is not intended to limit the scope of the embodiments, as claimed, but is merely representative of example embodiments.

[0010] Reference throughout this specification to“one embodiment” or“an embodiment” (or the like) means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearance of the phrases“in one embodiment” or“in an embodiment” or the like in various places throughout this specification are not necessarily all referring to the same embodiment.

[0011] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a thorough understanding of embodiments. One skilled in the relevant art will recognize, however, that the various embodiments can be practiced without one or more of the specific details, or with other methods, components, materials, et cetera. In other instances, well known structures, materials, or operations are not shown or described in detail to avoid obfuscation.

[0012] One component of coke waste water that is hazardous, and, therefore, desirable to be removed, is ammonia. To remove the ammonia the waste water is sent through a distillation column. In the distillation column alkali (caustic or lime) is added to the waste water to convert the ammonia to a different state, for example, from NH₄ to NH₃. The ammonia in the form of NH₃ can be distilled from the water with steam and/or heat. In other words, once the ammonia is converted to NH₃, the ammonia can be stripped from the water. This stripped ammonia can then be put into a gas phase which can be safely treated in concentrate form. The remaining waste water is then treated with biological aerated sludge systems to remove the lower level of ammonia that remains after the distillation process. As a merely illustrative example, the waste water coming into the distillation column may have 1 ,000 ppm (parts-per-million) of ammonia and the waste water leaving the distillation column may have 100 ppm of ammonia. Each system operator has a preferred level of ammonia that will be left after the distillation process. Thus, operators of the system attempt to optimize the amount of alkali (caustic or lime) and steam that is used to effectively and efficiently reduce the ammonia to preferred levels. [0013] In order to optimize the system, the system operators must know how much ammonia is left after the distillation process is complete. Traditional techniques for identifying the amount of ammonia that is left after the distillation process are manual techniques. Specifically, an operator or other user has to manually take a sample from the waste water discharge from the distillation column, otherwise referred to as the effluent side of the distillation column. This sample is then sent to a lab which then performs tests and analysis to determine the level of ammonia. The results of the test are then communicated to the operator who can then adjust the level of alkali and/or steam as needed. These tests can take hours or even days to perform and determine the results. Thus, these traditional techniques are ineffective and inefficient and may result in many hours or days of inefficient ammonia processing, which may result in the use of extra resources, either in the distillation column or during the subsequent treatment of the effluent of the distillation column.

[0014] One reason that these tests have to be performed manually is because traditional measurement devices that can be placed in-line with fluid sources are not designed to withstand the harsh chemistry of the waste water. In other words, the waste water has a very harsh chemistry that would cause traditional measurement devices to foul which results in measurement devices that either do not function or that provide highly inaccurate readings. Thus, the tests that are performed on waste water are manual wet tests that are performed in a laboratory setting. Additionally, traditional automated sensors are unable to measure the high levels of ammonia that is present in the waste water from the coke production.

[0015] Knowing the amount of targeted contaminants to be removed can allow for automation of the process in relation to the contaminant. More specifically, being able to correlate ammonia nitrogen with total organic nitrogen can allow for proactive automation of alkali (caustic or lime) and steam feed to the distillation column. Proactive feed of alkali and steam will allow for improved overall removal efficiency at the lowest operational cost.

[0016] Accordingly, an embodiment provides a method for measuring an amount of ammonia in an aqueous sample of waste water near a distillation column. The measurement may be performed either on the waste water before entering the distillation column or on the waste water after leaving the distillation column. In other words, the described measurement may be performed on either the influent or the effluent of the distillation column. The system and method obtains an aqueous sample of the waste water, either before the distillation column or after the distillation column, and uses a measurement device to measure an amount of nitrogen in the waste water. The measurement device is a measurement device that can withstand the harsh water chemistry of the waste water and that can measure the high levels of ammonia that is present in the waste water from the coke production.

[0017] Once the measurement device has measured the amount of nitrogen in the waste water, the system can identify an amount of ammonia in the waste water by correlating the amount of nitrogen to an amount of ammonia ln other words, ammonia is the highest contributor or source of nitrogen in the waste water. Therefore, the system is able to perform calculations based upon the amount of measured nitrogen to determine the amount of ammonia that is present in the waste water. Based upon the amount of ammonia in the waste water, the system can provide a feedback to the distillation column to adjust an amount of alkali and/or steam applied in the distillation column, if appropriate as identified by the ammonia measurement results.

[0018] The illustrated example embodiments will be best understood by reference to the figures. The following description is intended only by way of example, and simply illustrates certain example embodiments.

[0019] This disclosure is directed to on-line analytical measurement of nitrogen compounds in and/or out of a distillation (still) column in order to optimize the overall removal of ammonia. The use of the HACH BlOTECTOR, discussed in more detail below, allows for an approximation of total organic nitrogen levels to be determined and subsequent use of a programmable logic controller (PLC) to control steam and/or alkali treatment (critical parameters for steam stripping of the ammonia). Manual control of steam and/or alkali can also be optimized with the use of this data. Substantial savings in steam and alkali costs for still operation can be achieved with additional savings found in the area of post treatment and/or discharge surcharges to a sanitary outfall. HACH is a registered trademark of Hach Company in the United States and other countries.

BIOTECTOR is a registered trademark of Analytical Developments Limited in the United States and other countries.

[0020] Treatment of waste ammonia liquor (WAL) typically involves feeding the liquor to one of the top trays of the distillation column (ammonia still), injecting steam counter current to liquor flow and feeding an alkaline chemical to free up the ammonia (convert fixed ammonia to free ammonia which is strippable using steam). The injected steam increases the ammonia volatility so it strips out of the WAL into the departing gas vapor exiting the top of the still. The bottom liquor, now lean in ammonia, is pumped from the bottom of the still to be processed further, typically in a biological treatment plant, discharged to a sanitary sewer, or the like. Typical levels of nitrogen compounds entering and exiting and the still are:

[0021 ] The major nitrogen component stripped in the ammonia still is ammonia.

The other compounds are fairly stable across the still (accounting for steam dilution) with their mass balance not changing significantly as a“whole” relative to the ammonia, especially with liquor equalization tanks upstream. Therefore, TK-N and NH₃-N chemistry in and out of the still can be used as an indicator of still performance. Routine analytical wet testing can be used to predict still effluent TK-N levels as a function of ammonia removal efficiency in the still, knowing that the other forms of total nitrogen will be fairly constant for a few days or more. The use of the HACH BIOTECTOR will provide measurement of total nitrogen levels on-line, which is not conventionally possible, nor possible with conventional measurement devices or sensors.

[0022] Since the above tests are wet tests and are manually performed typically once a day or a few times a week, they do not lend themselves to being used for automation of the still. Other instruments for ammonia test have not proven to be reliable and/or accurate in WAL applications and eventually become unreliable and high maintenance.

[0023] The use of the on-line total nitrogen analyzer can allow for the potential feed forward and/or feedback control strategy for operation of the WAL still. Alkali feed and steam stripping rates can be adjusted proactively based upon knowing influent and/or effluent total nitrogen levels. Use of a PLC with proper programming for nitrogen levels, steam rates, alkali feed, and pH can be used proactively to control and optimize the overall performance of the still. Even manual adjustments can be made by operators to improve performance using the information obtained from the on-line nitrogen analyzer. Therefore, overall benefits of the described systems and methods include lower manpower to operate, lower analytical chemistry cost, lower steam cost, lower alkali treatment cost, and lower post treatment cost.

[0024] FIG. 1 illustrates a method for measuring an amount of ammonia in an aqueous sample of waste water from a distillation column. At 101 the system obtains an aqueous sample comprising waste water near a distillation column. The aqueous sample can be obtained from either the influent or the effluent of the distillation column. In the event that the aqueous sample is obtained before the distillation column the system the feedback to the system, as described in more detail below, can occur before the waste water enters the distillation column. In the event that the aqueous sample is obtained after the distillation column, the feedback to the system can occur for subsequent incoming waste water into the distillation column.

[0025] To obtain the aqueous sample the system may include a branch, valve, tap, or other pipe division, from the waste water pipe. For ease of readability, this pipe division will be referred to as a branch. However, this is not intended to limit the system to only a pipe branch and other pipe divisions are contemplated and possible. This branch may be of a smaller diameter than the waste water pipe. This smaller diameter may result in a particular fluid flow that may be, but is not exclusively, necessary for the

measurement device. In-line with the branch may be a measurement device. As the waste water flows through the branch, the measurement device may capture a small amount of the waste water in order to perform the necessary measurements. This small amount of waste water captured or obtained by the measurement device is referred to as the aqueous sample.

[0026] The measurement device may be an on-line process-measurement device that is specifically designed to withstand the harsh chemistry of the waste water without fouling, unlike traditional sensors or measurement devices. Additionally, the

measurement device may be designed to measure high levels of ammonia and provide a quick measurement reading, also unlike traditional sensors or measurement devices or laboratory measurement methods. An example of such a device may be a the HACH BIOTECTOR online Total Organic Carbon (TOC), Total Nitrogen (TN), and Total Phosphorus (TP) Analyzer, available from Hach Company, Loveland, CO. BIOTECTOR is a registered trademark of Analytical Developments Limited in the United States and other countries. Details of the BIOTECTOR can be found in United States Patent 8,91 1,692, issued on December 16, 2014, United States Patent 7,556,773, issued on July 7, 2009, United States Patent 7,556,772, issued on July 7, 2009, United States Patent 6,623,974, issued on September 23, 2003, and United States Patent Application

15/663,732, filed on July 29, 2017, the contents of all of which are incorporated by reference herein. The above listed BIOTECTOR patents and applications describe a device that can measure total organic carbon (TOC), total nitrogen, and total phosphorous of an aqueous sample. The above described BIOTECTOR is designed to withstand harsh fluid chemistries and can provide measurements of high levels of different compounds. The HACH BIOTECTOR provides reliable, continuous monitoring and real-time process control. The HACH BIOTECTOR uses a two-stage advanced oxidation technology that handles even the most challenging applications involving fats, oils, greases, salts, sludges, and particulates. Thus, at 102, the measurement device may measure an amount of nitrogen in the obtained aqueous sample. [0027] At 103 the system may identify an amount of ammonia in the aqueous sample based upon the measured amount of nitrogen. The highest source of nitrogen in the waste water sample is ammonia. Thus, the majority of the nitrogen in the aqueous sample is attributable to ammonia in the waste water. Additionally, the other sources of nitrogen in the waste water are known sources that provide a steady level of nitrogen. Therefore, the system may be calibrated using the known levels nitrogen provided by those other sources. In other words, based upon the known nitrogen levels that are produced by background nitrogen sources, the system may zero the system based upon the known levels, subtract the known levels before calculating the level of ammonia, or otherwise account for the nitrogen levels provided by the sources other than ammonia. Using the measured nitrogen levels, minus the nitrogen levels of sources other than ammonia, the system may correlate the nitrogen levels to an amount of ammonia in the waste water. In other words, there is a mathematical relationship between the level of nitrogen and the level of ammonia in the waste water. For example, the relationship may be a proportional relationship between the nitrogen and the ammonia. However, other relationships between the levels of nitrogen and ammonia may be present. Using the determined relationship, the system can calculate the level of ammonia in the waste water. [0028] At 104 the system may determine whether the alkali (caustic or lime) and/or steam of the distillation column should be adjusted based upon the amount of ammonia in the aqueous sample. In other words, based upon the amount of ammonia in the aqueous sample, the system may provide feedback to the distillation column, distillation column system, or operator of the distillation column to optimize the amount of alkali and/or steam that is added at the distillation column to efficiently and effectively reduce the amount of ammonia in the waste water to the desired levels upon exiting the distillation column. To determine if the alkali (caustic or lime) and/or steam should be adjusted the system may compare the identified ammonia levels to a threshold value. For example, if the system operator has a specific value or level of ammonia that is considered acceptable in the effluent the system may compare the identified amount of ammonia to that specified value. If the identified amount of ammonia is above that specified value, the system may provide an indication to adjust the alkali and/or steam that is applied in the distillation column. The system may also identify an amount of alkali and/or steam that is required to reach the desired threshold.

[0029] In the case that the measurement is taken on the influent side of the distillation column, the system may calculate an amount of alkali (caustic or lime) and/or steam that should be applied in order to reduce the level of ammonia to a desired value. For example, the system may include one or more tables that identify how much alkali and/or steam would be required to reduce the level of ammonia a particular amount. The system may then perform a calculation to identify the required amount of alkali and/or steam that would be necessary to reduce the identified amount of ammonia to the desired level. If an adjustment is needed at 104, for example, either based upon an influent or effluent measurement, the system may provide an indication of the adjustment to the distillation column, a system coupled to the distillation column, an operator of the distillation column, or the like. For example, the indication may be a notification to an operator to adjust the level of alkali and/or steam. As another example, the indication may be a signal to the distillation column or system of the distillation column to adjust the level of alkali and/or steam. If an adjustment is not needed, the system may provide an indication that an adjusted is not needed at 106. Alternatively, the system may take no action in the case that an adjustment is not needed.

[0030] The various embodiments described herein thus represent a technical improvement to current manual ammonia measurement techniques. Rather than having to manually take a sample from the effluent of the distillation column, the system provides an automated technique that can capture a sample and take measurements. Additionally, since the described measurement device can withstand harsh fluid chemistry and take measurements of high levels of nitrogen, which are not possible using conventional sensors and/or measurement devices, the system provides an in-line method for calculating ammonia levels in the waste water. Based upon these measurements the system can provide near real-time feedback to the distillation column regarding the level of alkali (caustic or lime) and/or steam that is applied in the distillation column to optimize the removal of ammonia in the waste water. Such a near real-time feedback is not possible with conventional methods that require taking a sample and sending it to a lab for analysis which may take many hours, days, or even weeks. Thus, the systems and methods as described herein provide an efficient, effective, and optimized system for ammonia measurement near a distillation column.

[0031] While various other circuits, circuitry or components may be utilized in information handling devices, with regard to an instrument for measuring fluid level and velocity according to any one of the various embodiments described herein, an example is illustrated in FIG. 2. Device circuitry 200 may include a measurement system on a chip design found, for example, a particular computing platform (e.g., mobile computing, desktop computing, etc.) Software and processor(s) are combined in a single chip 201. Processors comprise internal arithmetic units, registers, cache memory, busses, I/O ports, etc., as is well known in the art. Internal busses and the like depend on different vendors, but essentially all the peripheral devices (202) may attach to a single chip 201. The circuitry 200 combines the processor, memory control, and I/O controller hub all into a single chip 410. Common interfaces may include SPI, I2C and SDIO. [0032] There are power management chip(s) 203, e.g., a battery management unit, BMU, which manage power as supplied, for example, via a rechargeable battery 204, which may be recharged by a connection to a power source (not shown). In at least one design, a single chip, such as 201, is used to supply BIOS like functionality and DRAM memory.

[0033] System 200 typically includes one or more of a WWAN transceiver 205 and a WLAN transceiver 206 for connecting to various networks, such as

telecommunications networks and wireless Internet devices, e.g., access points.

Additionally, devices 202 are commonly included, e.g., a transmit and receive antenna, oscillators, PLLs, etc. System 200 includes input/output devices 207 for data input and display/rendering (e.g., a computing location located away from the single beam system that is easily accessible by a user). System 200 also typically includes various memory devices, for example flash memory 208 and SDRAM 209.

[0034] It can be appreciated from the foregoing that electronic components of one or more systems or devices may include, but are not limited to, at least one processing unit, a memory, and a communication bus or communication means that couples various components including the memory to the processing unit(s). A system or device may include or have access to a variety of device readable media. System memory may include device readable storage media in the form of volatile and/or nonvolatile memory such as read only memory (ROM) and/or random access memory (RAM). By way of example, and not limitation, system memory may also include an operating system, application programs, other program modules, and program data.

[0035] Embodiments may be implemented as an instrument, system, method or program product. Accordingly, an embodiment may take the form of an entirely hardware embodiment, or an embodiment including software (including firmware, resident software, micro-code, etc.) that may all generally be referred to herein as a“circuit,” “module” or“system.” Furthermore, embodiments may take the form of a program product embodied in at least one device readable medium having device readable program code embodied thereon.

[0036] A combination of device readable storage medium(s) may be utilized. In the context of this document, a device readable storage medium (“storage medium”) may be any tangible, non-signal medium that can contain or store a program comprised of program code configured for use by or in connection with an instruction execution system, apparatus, or device. For the purpose of this disclosure, a storage medium or device is to be construed as non-transitory, i.e., not inclusive of signals or propagating media. [0037] This disclosure has been presented for purposes of illustration and description but is not intended to be exhaustive or limiting. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiments were chosen and described in order to explain principles and practical application, and to enable others of ordinary skill in the art to understand the disclosure for various embodiments with various modifications as are suited to the particular use contemplated.

[0038] Thus, although illustrative example embodiments have been described herein with reference to the accompanying figures, it is to be understood that this description is not limiting and that various other changes and modifications may be affected therein by one skilled in the art without departing from the scope or spirit of the disclosure.

Claims

CLAIMS What is claimed is:

1. A method for measuring ammonia in waste water near a distillation column, comprising: obtaining an aqueous sample comprising waste water near a distillation column; measuring, using a nitrogen measurement device that performs oxidation of components of the aqueous sample, an amount of nitrogen in the obtained aqueous sample to provide real-time nitrogen measurement; identifying an amount of ammonia in the aqueous sample, wherein the identifying comprises correlating the measured amount of nitrogen to an amount of ammonia; and adjusting, based upon the identified amount of ammonia, a level of alkali injected into the distillation column and an amount of steam applied at the distillation column.

2. The method of claim 1, wherein the obtaining an aqueous sample comprises obtaining an aqueous sample before the waste water enters the distillation column.

3. The method of claim 1 , wherein the obtaining an aqueous sample comprises obtaining an aqueous sample after the waste water leaves the distillation column.

4. The method of claim 1, wherein the measuring comprises utilizing an on-line total nitrogen analyzer.

5. The method of claim 1, wherein the identifying comprises subtracting nitrogen values attributable to known sources from the measured amount of nitrogen.

6. The method of claim 1 , wherein the identifying comprises zeroing a measurement system utilizing nitrogen values attributable to known sources from the measured amount of nitrogen

7. The method of claim 1 , wherein the measured amount of nitrogen is proportional to the amount of ammonia.

8. The method of claim 1 , wherein the adjusting comprises comparing the identified amount of ammonia to a threshold value and adjusting the level of alkali and the amount of steam based upon the comparing.

9. The method of claim 8, wherein the adjusting comprises adjusting the level of alkali and the amount of steam so that the amount of ammonia reaches the threshold value.

10. The method of claim 8, wherein the adjusting the level of alkali and the amount of steam comprises increasing one of: the level of alkali and the amount of steam based upon the amount of ammonia being greater than the threshold value.

1 1. A system for measuring ammonia in waste water near a distillation column, comprising: a nitrogen measurement device; a processor; and a memory device that stores instructions executable by the processor to: obtain an aqueous sample comprising waste water near a distillation column; measure, using the nitrogen measurement device that performs oxidation of components of the aqueous sample, an amount of nitrogen in the obtained aqueous sample to provide real-time nitrogen measurement; identify an amount of ammonia in the aqueous sample, wherein the identifying comprises correlating the measured amount of nitrogen to an amount of ammonia; and adjust, based upon the identified amount of ammonia, a level of alkali injected into the distillation column and an amount of steam applied at the distillation column.

12. The system of claim 11, wherein the obtaining an aqueous sample comprises obtaining an aqueous sample before the waste water enters the distillation column.

13. The system of claim 11, wherein the obtaining an aqueous sample comprises obtaining an aqueous sample after the waste water leaves the distillation column.

14. The system of claim 11, wherein the measuring comprises utilizing an on-line total nitrogen analyzer.

15. The system of claim 1 1, wherein the identifying comprises subtracting nitrogen values attributable to known sources from the measured amount of nitrogen.

16. The system of claim 11, wherein the identifying comprises zeroing a measurement system utilizing nitrogen values attributable to known sources from the measured amount of nitrogen

17. The system of claim 11, wherein the measured amount of nitrogen is proportional to the amount of ammonia.

18. The system of claim 11, wherein the adjusting comprises comparing the identified amount of ammonia to a threshold value and adjusting the level of alkali and the amount of steam based upon the comparing.

19. The system of claim 18, wherein the adjusting comprises adjusting the level of alkali and the amount of steam so that the amount of ammonia reaches the threshold value.

20. The system of claim 18, wherein the adjusting the level of alkali and the amount of steam comprises increasing one of: the level of alkali and the amount of steam based upon the amount of ammonia being greater than the threshold value.