A method for treating glycine dealcoholation mother liquor

Abstract

The present application relates to a method for treating a glycine dealcoholation mother liquor, comprising the following steps: subjecting the glycine dealcoholation mother liquor to a first-stage multi-effect evaporator for evaporation treatment, recovering the ammonium chloride therein to obtain a first-stage condensed water; adding hydrochloric acid to the first-stage condensed water to adjust the pH value; subjecting the pH-adjusted first-stage condensed water to a second-stage multi-effect evaporator for evaporation treatment, recovering the ammonium chloride therein to obtain a second-stage condensed water; returning the second-stage condensed water to a chloroacetic acid method for producing glycine, and discharging excess second-stage condensed water into a biochemical system; wherein the heating temperature range of the first-stage multi-effect evaporator is 90°C-110°C; and the heating temperature range of the second-stage multi-effect evaporator is 55°C-90°C. The present application provides a method for treating a glycine dealcoholation mother liquor, which can effectively reduce the ammonia nitrogen content and chloride content in glycine wastewater, meeting environmental emission standards and reuse standards.

Description

Technical Field

[0001] The present application relates to the technical field of glycine production, and in particular to a method for treating glycine dealcoholation mother liquor. Background Art

[0002] Glycine (Gly), also known as aminoacetic acid, is a non-essential amino acid. It is a component of the endogenous antioxidant reduced glutathione and is often supplemented exogenously during periods of severe stress. It is sometimes called a semi-essential amino acid. Glycine is the simplest amino acid and an important chemical intermediate, widely used in pharmaceuticals, pesticides, organic synthesis, and biochemical synthesis.

[0003] At present, more than 85% of glycine in China is produced by the chloroacetic acid ammoniation process. The process is as follows: using water as a solvent and hexamine as a catalyst, chloroacetic acid and ammonia are reacted to form a mixture of glycine and ammonium chloride. A large amount of methanol is then added for alcohol precipitation. After centrifugation, a mother liquor containing mixed components such as ammonium chloride, glycine, hexamine, water, and methanol is separated out to obtain glycine solid. The centrifuged mother liquor after the glycine separation is distilled to recover methanol to obtain a glycine dealcoholization mother liquor. The glycine dealcoholization mother liquor is evaporated to recover ammonium chloride. The ammonium chloride recovery process generates evaporated condensed water. If this evaporated condensed water is reused in glycine production, it will affect the quality of the glycine product. Secondly, even if it is reused in glycine production, the large amount of evaporated condensed water cannot be digested and finally enters the biochemical system for treatment. On the other hand, the concentration also produces high-concentration red wastewater (commonly known as "red water"), which has a complex composition, a variety of pollutants, a high concentration, high ammonia nitrogen and high COD, making it difficult to enter the biochemical system for biochemical treatment. Therefore, solving the problem of glycine dealcoholization mother liquor and then solving the problem of glycine wastewater treatment has become an urgent issue that glycine production companies need to solve. Summary of the Invention

[0004] The invention provides a method for treating glycine dealcoholation mother liquor, so as to solve the technical problem that glycine wastewater has excessive ammonia nitrogen content and is difficult to enter a biochemical system for biochemical treatment.

[0005] The present invention provides a method for treating a glycine dealcoholation mother liquor, comprising the following steps:

[0006] Step S1, subjecting the glycine dealcoholation mother liquor to a first-stage multi-effect evaporator for evaporation to recover ammonium chloride to obtain first-stage condensed water;

[0007] Step S2, adding hydrochloric acid to the first-level condensed water to adjust the pH value;

[0008] Step S3, subjecting the pH-adjusted primary condensed water to a second-stage multi-effect evaporator for evaporation to recover ammonium chloride to obtain secondary condensed water;

[0009] Step S4: returning the secondary condensed water to the chloroacetic acid process for producing glycine, and discharging excess secondary condensed water into the biochemical system;

[0010] Among them, the temperature range of the first-stage multi-effect evaporator is 90℃-110℃; the temperature range of the second-stage multi-effect evaporator is 65℃-90℃.

[0011] The present invention adds hydrochloric acid to adjust the pH value of the glycine dealcoholation mother liquor after it has been evaporated and ammonium chloride has been recovered in a first-stage multi-effect evaporator, rather than directly adding hydrochloric acid to the glycine dealcoholation mother liquor to adjust the pH value. This is because wastewater contains a large amount of ammonium chloride, and using hydrochloric acid to adjust the pH value before multi-effect evaporation will consume a large amount of hydrochloric acid. In addition, a large amount of ammonia will still be absorbed by evaporated condensed water during the multi-effect evaporation process, resulting in an increase in ammonia nitrogen. This cannot effectively solve the technical problem that the ammonia nitrogen value of the treated wastewater is still too high to be able to enter the biochemical system for treatment.

[0012] The present invention adopts after glycine dealcoholation mother liquor is recovered ammonium chloride through triple-effect evaporation, then adds hydrochloric acid to adjust pH value, its principle is that the glycine dealcoholation mother liquor will produce a large amount of ammonia in triple-effect evaporation concentration deammonium chloride process, ammonia is very easily soluble in water (under normal temperature and pressure, 1 volume of water approximately dissolves 700 volumes of ammonia), can make the ammonia nitrogen content in the first-level condensed water up to 15000mg / L, now add hydrochloric acid to adjust pH value after making the ammonia in the first-level condensed water react with hydrochloric acid to form ammonium chloride, ammonia is locked in water, carry out multiple-effect evaporation and concentrate when ammonium chloride concentration is not high, the ammonia produced by decomposition can be reduced in a large number, now the second-level multiple-effect evaporation temperature is significantly reduced compared to the first-level multiple-effect evaporation temperature, liquid pH is below 5, and ammonia is also difficult for evaporation under this condition. Therefore, the ammonia nitrogen content of the secondary condensed water will only decrease significantly, now, chloride content also significantly decreases, even without, after re-concentration, low-chlorine and low-ammonia nitrogen wastewater can not only be returned to the workshop for use, and the excess part can also directly enter the living system for processing. It also solves the problem of excessive chloride content in the recycled glycine system's water affecting the quality of glycine products.

[0013] Specifically, the first-stage multi-effect evaporator is a triple-effect evaporator, and the evaporation is low-temperature negative pressure evaporation. The heating temperature of the first-effect evaporator is 100℃-110℃, the heating temperature of the second-effect evaporator is 95℃-100℃, and the heating temperature of the third-effect evaporator is between 90℃-95℃. The pressure range is -0.03MPa—0.06MPa.

[0014] Specifically, the second-stage multi-effect evaporator is a triple-effect evaporator, the evaporation is low-temperature negative pressure evaporation, the heating temperature of the first-effect evaporator is 80℃-90℃, the heating temperature of the second-effect evaporator is 75℃-85℃, the heating temperature of the third-effect evaporator is between 55℃-65℃, and the pressure range is -0.06MPa-0.09MPa.

[0015] Specifically, hydrochloric acid is used to adjust the pH value to no greater than 5, such as pH = 1, pH = 2, pH = 3, pH = 4, pH = 5, etc. The mass concentration of the hydrochloric acid is 30%-33%, such as 30%, 31%, 32%, 33%, etc. In particular, the hydrochloric acid is derived from hydrochloric acid produced as a by-product of chloroacetic acid produced by the catalytic chlorination of acetic acid, and is used to recycle the hydrochloric acid produced as a by-product of chloroacetic acid produced by the catalytic chlorination of acetic acid for glycine production, but commercially available sources are not excluded.

[0016] Specifically, the first-stage multiple-effect evaporator or the second-stage multiple-effect evaporator can be multiple sets of multiple-effect evaporators. Depending on the amount of glycine dealcoholation mother liquor to be processed, multiple sets of first-stage multiple-effect evaporators can be deployed to simultaneously process a large amount of glycine dealcoholation mother liquor. For example, three sets of first-stage multiple-effect evaporators can be deployed in parallel to simultaneously process the glycine dealcoholation mother liquor. Similarly, multiple sets of second-stage multiple-effect evaporators can be deployed accordingly.

[0017] Specifically, the chloride content by mass in the treated secondary condensed water is less than 0.1%. At this time, returning the treated secondary condensed water to the chloroacetic acid method glycine production system will not affect the quality of the glycine product.

[0018] Specifically, the treated secondary condensate has an ammonia nitrogen content of less than 500 mg / L. The treated secondary condensate is returned to the chloroacetic acid process glycine production system as unconsumable secondary condensate wastewater, which has an ammonia nitrogen content of less than 500 mg / L and does not affect discharge into the biochemical system for treatment.

[0019] The beneficial effects of the technical solution provided by this application include:

[0020] (1) The present application uses hydrochloric acid to adjust the pH of the first condensed water after recovering ammonium chloride by performing the first-stage triple-effect evaporation on the glycine dealcoholation mother liquor, so that the ammonia dissolved in the water is locked in the water in the form of ammonium chloride, and the ammonia produced by decomposition is greatly reduced, so that the ammonia nitrogen content of the secondary condensed water is significantly reduced, and the chloride content is also significantly reduced, or even eliminated, so that the treated glycine wastewater is returned to the glycine production system without affecting the quality of glycine, and the excess water can also be discharged into the biochemical system for treatment, meeting the environmental discharge and reuse standards;

[0021] (2) The first-stage condensed water produced by this method can be returned to the production system for recycling after treatment, without affecting the glycine product index, and the excess wastewater can be discharged in compliance with the standards;

[0022] (3) This method can effectively reduce the final waste liquid (commonly known as "red water") generated by separating ammonium chloride and reduce the cost of treating the waste liquid;

[0023] (4) This method is simple to operate and has a large wastewater treatment capacity. The amount of wastewater after treatment can be effectively treated to ensure the normal production of glycine. DETAILED DESCRIPTION

[0024] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0025] Example 1

[0026] The glycine dealcoholation mother liquor was subjected to a first-stage triple-effect evaporation to recover ammonium chloride, and the ammonium chloride was recovered by sequentially passing through a first-effect evaporation system (temperature 100° C., pressure -0.04 MPa), a second-effect evaporation system (temperature 95° C., pressure -0.05 MPa), and a third-effect evaporation system (temperature 90° C., pressure -0.06 MPa) to obtain a first-stage condensed water with an ammonia nitrogen content of 14125 mg / L and a chloride mass percentage of 0.78%;

[0027] The pH of the primary condensate is adjusted to 2 using 33% hydrochloric acid, a byproduct of the chloroacetic acid production process using acetic acid catalytic chlorination. The adjusted glycine dealcoholation mother liquor undergoes a second-stage triple-effect evaporation to recover ammonium chloride. The evaporation is sequentially processed through a first-effect evaporation system (temperature 90°C, pressure -0.06 MPa), a second-effect evaporation system (85°C, pressure -0.07 MPa), and a third-effect evaporation system (temperature 65°C, pressure -0.08 MPa) to obtain secondary condensate with an ammonia nitrogen content of 387 mg / L and a chloride content of 0.065%. The secondary condensate is then returned to the glycine production system using the chloroacetic acid process to obtain industrial glycine with a mass fraction of 98.50%.

[0028] Example 2

[0029] The glycine dealcoholation mother liquor was subjected to a first-stage triple-effect evaporation to recover ammonium chloride, and the ammonium chloride was recovered by sequentially passing through a first-effect evaporation system (temperature 110° C., pressure -0.03 MPa), a second-effect evaporation system (temperature 100° C., pressure -0.04 MPa), and a third-effect evaporation system (temperature 95° C., pressure -0.05 MPa) to obtain a first-stage condensed water having an ammonia nitrogen content of 13580 mg / L and a chloride mass percentage of 0.69%;

[0030] The pH of the primary condensate was adjusted to 4 using 31% hydrochloric acid, a byproduct of the chloroacetic acid production process using acetic acid catalytic chlorination. The adjusted pH of the glycine dealcoholation mother liquor was then subjected to a second-stage triple-effect evaporation process to recover ammonium chloride. The evaporation was sequentially processed through a first-effect evaporation system (temperature 85°C, pressure -0.07 MPa), a second-effect evaporation system (80°C, pressure -0.07 MPa), and a third-effect evaporation system (temperature 65°C, pressure -0.08 MPa) to obtain secondary condensate with an ammonia nitrogen content of 371 mg / L and a chloride content of 0.023%. The secondary condensate was then returned to the chloroacetic acid process to produce glycine, yielding industrial glycine with a mass fraction of 98.55%.

[0031] Example 3

[0032] The glycine dealcoholation mother liquor was subjected to a first-stage triple-effect evaporation to recover ammonium chloride, and the ammonium chloride was recovered by sequentially passing through a first-effect evaporation system (temperature 105° C., pressure -0.04 MPa), a second-effect evaporation system (temperature 95° C., pressure -0.05 MPa), and a third-effect evaporation system (temperature 90° C., pressure -0.06 MPa) to obtain a first-stage condensed water having an ammonia nitrogen content of 14100 mg / L and a chloride mass percentage of 0.72%;

[0033] The pH of the primary condensate was adjusted to 5 using 30% hydrochloric acid. The adjusted glycine dealcoholation mother liquor was subjected to a second-stage triple-effect evaporation to recover ammonium chloride. The evaporation was sequentially carried out through a first-effect evaporation system (temperature 80°C, pressure -0.07 MPa), a second-effect evaporation system (75°C, pressure -0.08 MPa), and a third-effect evaporation system (temperature 55°C, pressure -0.09 MPa) to obtain secondary condensate with an ammonia nitrogen content of 314 mg / L and a chloride content of 0.005%. The secondary condensate was then returned to the chloroacetic acid process for glycine production, yielding industrial glycine with a mass fraction of 98.53%.

[0034] Example 4

[0035] The glycine dealcoholation mother liquor is subjected to the first stage triple-effect evaporation to recover ammonium chloride, using two sets of triple-effect evaporation systems;

[0036] The first set of condensed water is obtained by sequentially passing through the first-effect evaporation system (temperature 105°C, pressure -0.04MPa), the second-effect evaporation system (temperature 95°C, pressure -0.05MPa), and the third-effect evaporation system (temperature 90°C, pressure -0.06MPa).

[0037] The second set of condensed water is obtained by sequentially passing through the first-effect evaporation system (temperature 110°C, pressure -0.03MPa), the second-effect evaporation system (temperature 100°C, pressure -0.04MPa), and the third-effect evaporation system (temperature 95°C, pressure -0.05MPa).

[0038] The first-stage condensate of the combined two triple-effect evaporation systems has an ammonia nitrogen content of 13902 mg / L and a chloride mass percentage of 0.68%;

[0039] The pH of the primary condensate is adjusted to 3 using 31% hydrochloric acid. The adjusted glycine dealcoholation mother liquor is then subjected to a second-stage triple-effect evaporation to recover ammonium chloride. The evaporation is sequentially processed through a first-effect evaporation system (temperature 85°C, pressure -0.07 MPa), a second-effect evaporation system (80°C, pressure -0.07 MPa), and a third-effect evaporation system (temperature 65°C, pressure -0.08 MPa) to obtain secondary condensate with an ammonia nitrogen content of 357 mg / L and a chloride content of 0.014% by mass. The secondary condensate is returned to the chloroacetic acid process for glycine production, yielding an industrial glycine concentration of 98.54%. Excess secondary condensate can be discharged to a biochemical system for treatment.

[0040] Example 5

[0041] The glycine dealcoholation mother liquor was subjected to a first-stage triple-effect evaporation to recover ammonium chloride, and the ammonium chloride was recovered by sequentially passing through a first-effect evaporation system (temperature 105° C., pressure -0.04 MPa), a second-effect evaporation system (temperature 94° C., pressure -0.05 MPa), and a third-effect evaporation system (temperature 92° C., pressure -0.06 MPa) to obtain a first-stage condensed water having an ammonia nitrogen content of 15003 mg / L and a chloride mass percentage of 0.80%;

[0042] The pH value of the first-stage condensed water is adjusted to 2 with 33% hydrochloric acid, and the adjusted glycine dealcoholation mother liquor is subjected to a second-stage triple-effect evaporation to recover ammonium chloride, using two sets of triple-effect evaporation systems;

[0043] The first set of condensed water is obtained by sequentially passing through the first-effect evaporation system (temperature of 90°C and pressure of -0.06MPa), the second-effect evaporation system (85°C and pressure of -0.07MPa), and the third-effect evaporation system (temperature of 65°C and pressure of -0.08MPa).

[0044] The second set of condensed water is obtained by sequentially passing through the first-effect evaporation system (temperature of 80°C and pressure of -0.07MPa), the second-effect evaporation system (75°C and pressure of -0.08MPa), and the third-effect evaporation system (temperature of 55°C and pressure of -0.09MPa) to obtain the first set of secondary condensed water;

[0045] The combined secondary condensate from the two triple-effect evaporation systems had an ammonia nitrogen content of 367 mg / L and a chloride mass percentage of 0.045%. This secondary condensate was returned to the chloroacetic acid process for glycine production, yielding an industrial glycine mass fraction of 98.52%.

[0046] Comparative Example 1

[0047] The glycine dealcoholation mother liquor was subjected to a first-stage triple-effect evaporation to recover ammonium chloride, and the ammonium chloride was recovered by sequentially passing through a first-effect evaporation system (temperature 110° C., pressure -0.03 MPa), a second-effect evaporation system (temperature 100° C., pressure -0.04 MPa), and a third-effect evaporation system (temperature 95° C., pressure -0.05 MPa) to obtain a first-stage condensed water having an ammonia nitrogen content of 13580 mg / L and a chloride mass percentage of 0.69%;

[0048] The first-stage condensed water was subjected to a second-stage triple-effect evaporation to recover ammonium chloride, and sequentially passed through the first-effect evaporation system (temperature of 85°C, pressure of -0.07 MPa), the second-effect evaporation system (80°C, pressure of -0.07 MPa), and the third-effect evaporation system (temperature of 65°C, pressure of -0.08 MPa) to obtain secondary condensed water with an ammonia nitrogen content of 11423 mg / L and a chloride mass percentage of 0.57%.

[0049] Comparative Example 2

[0050] The glycine dealcoholation mother liquor was subjected to a first-stage triple-effect evaporation to recover ammonium chloride, and the ammonium chloride was recovered by sequentially passing through a first-effect evaporation system (temperature 100° C., pressure -0.04 MPa), a second-effect evaporation system (temperature 95° C., pressure -0.05 MPa), and a third-effect evaporation system (temperature 90° C., pressure -0.06 MPa) to obtain a first-stage condensed water with an ammonia nitrogen content of 14125 mg / L and a chloride mass percentage of 0.78%;

[0051] The pH value of the first-stage condensed water was adjusted to 2 using hydrochloric acid having a mass concentration of 33%, and the adjusted glycine dealcoholation mother liquor was subjected to a second-stage triple-effect evaporation to recover ammonium chloride. The condensed water was sequentially passed through a first-effect evaporation system (temperature of 100° C. and pressure of −0.04 MPa), a second-effect evaporation system (temperature of 95° C. and pressure of −0.05 MPa), and a third-effect evaporation system (temperature of 90° C. and pressure of −0.06 MPa) to obtain secondary condensed water with an ammonia nitrogen content of 8734 mg / L and a chloride mass percentage of 0.53%.

[0052] Comparative Example 3

[0053] The glycine dealcoholation mother liquor was subjected to a first-stage triple-effect evaporation to recover ammonium chloride. The ammonium chloride was recovered by sequentially passing through a first-effect evaporation system (temperature 110°C, pressure -0.03 MPa), a second-effect evaporation system (temperature 100°C, pressure -0.04 MPa), and a third-effect evaporation system (temperature 95°C, pressure -0.05 MPa) to obtain primary condensed water with an ammonia nitrogen content of 13580 mg / L and a chloride mass percentage of 0.69%.

[0054] The pH value of the primary condensed water was adjusted to 5 with hydrochloric acid having a mass concentration of 20%, and the adjusted glycine dealcoholation mother liquor was subjected to a second-stage triple-effect evaporation to recover ammonium chloride, and sequentially passed through a first-effect evaporation system (temperature of 85° C., pressure of −0.07 MPa), a second-effect evaporation system (80° C., pressure of −0.07 MPa), and a third-effect evaporation system (temperature of 65° C., pressure of −0.08 MPa) to obtain secondary condensed water. The amount of the secondary condensed water increased by 36% per liter compared to Example 2, and the additional wastewater treatment amount was increased, which correspondingly increased the additional energy consumption, which was not conducive to wastewater treatment.

[0055] As can be seen from the above examples and comparative examples, by adjusting the pH of the condensed water after the first triple-effect evaporation treatment and then performing a second triple-effect evaporation treatment, the ammonia nitrogen content in the condensed water can be significantly reduced, meeting the ammonia nitrogen standard for sewage treatment plants (ammonia nitrogen content less than 500 mg / L). At the same time, the chlorine content is less than 0.1%, meeting the reuse standard, without affecting the quality of the glycine product. Furthermore, the reduction of the ammonia nitrogen content in the condensed water can only be achieved by adopting a reasonable triple-effect evaporation temperature gradient setting.

[0056] It should be noted that, in this application, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprising a ..." does not exclude the presence of other identical elements in the process, method, article or device comprising the element.

[0057] The foregoing is merely a list of specific embodiments of the present application, intended to enable those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the broadest scope consistent with the principles and novel features of the present application.

Claims

1. A method for treating a glycine dealcoholation mother liquor, characterized in that: The following steps are involved: Step S1, subjecting the glycine dealcoholation mother liquor to a first-stage multi-effect evaporator for evaporation to recover ammonium chloride to obtain first-stage condensed water; Step S2, adding hydrochloric acid to the first-stage condensed water to adjust the pH value; using hydrochloric acid to adjust the pH value to no more than 5; Step S3, subjecting the pH-adjusted primary condensed water to a second-stage multiple-effect evaporator for evaporation to recover ammonium chloride to obtain secondary condensed water; Step S4: returning the secondary condensed water to the chloroacetic acid process for producing glycine, and discharging excess secondary condensed water into the biochemical system; Among them, the heating temperature range of the first-stage multi-effect evaporator is 90℃-110℃; the heating temperature range of the second-stage multi-effect evaporator is 55℃-90℃.

2. The method for treating a glycine dealcoholation mother liquor as claimed in claim 1, wherein The first-stage multi-effect evaporator is a triple-effect evaporator, and the evaporation is low-temperature negative pressure evaporation. The heating temperature of the first-effect evaporator is 100℃-110℃, the heating temperature of the second-effect evaporator is 95℃-100℃, and the heating temperature of the third-effect evaporator is between 90℃-95℃. The pressure range is -0.03MPa—0.06MPa.

3. The method for treating the glycine dealcoholation mother liquor as claimed in claim 1, wherein The second-stage multi-effect evaporator is a triple-effect evaporator, and the evaporation is low-temperature negative pressure evaporation. The heating temperature of the first-effect evaporator is 80°C-90°C, the heating temperature of the second-effect evaporator is 75°C-85°C, and the heating temperature of the third-effect evaporator is between 55°C-65°C. The pressure range is -0.06MPa-0.09MPa.

4. The method for treating the glycine dealcoholation mother liquor as claimed in claim 1, wherein The mass concentration of the hydrochloric acid is 30%-33%.

5. The method for treating the glycine dealcoholation mother liquor according to claim 1, wherein The hydrochloric acid is derived from the hydrochloric acid produced as a by-product in the production of chloroacetic acid by the catalytic chlorination of acetic acid.

6. The method for treating the glycine dealcoholation mother liquor according to claim 1, wherein The first-stage multiple-effect evaporator or the second-stage multiple-effect evaporator is a plurality of sets of multiple-effect evaporators.

7. The method for treating the glycine dealcoholation mother liquor according to claim 1, wherein The mass percentage of chloride in the treated secondary condensed water is less than 0.1%.

8. The method for treating the glycine dealcoholation mother liquor according to claim 1, wherein The ammonia nitrogen content in the treated secondary condensed water is less than 500 mg / L.