FIELD
The present disclosure relates to removing ammonia from battery liquor derived from coke plant or coal conversion, and particularly towards improvement of stripping efficiency of ammonia still for better remove ammonia and cyanide from battery liquor in form of both free and fixed by utilizing waste heat.
BACKGROUND
The battery liquor or wastewater from the Coke Oven during coal to coke conversion contains high amount of ammonia and cyanide along with other organic contaminants. This liquor is fed to the Ammonia Still for steam distillation to separate out ammonia and cyanide from the liquor. Moreover, sodium hydroxide (NaOH) is introduced during distillation to remove fixed ammonia and cyanide. For further removal of cyanide and ammonia amongst other impurities the treated liquor is sent to the Biological Oxygen Treatment (BOT) plant and followed by chemical treatment.
The pH of the battery liquor is around 9.5-10.5. During distillation, sodium hydroxide solution is fed to the ammonia still. Sodium hydroxide is used to remove fixed ammonia and cyanide from the liquor. However, it has been observed that after distillation the pH of the solution is nearly 8 to 8.5 though alkaline medium is introduced along with battery liquor. This phenomenon has ensured that the battery liquor is in the form of a “buffer”

having pH around 9.5 to 10.5 at a temperature of 40-50°C. From experimental study, it has been confirmed that if it were possible to break the buffer before the distillation by raising temperature, the consumption of NaOH would get reduced. In general, the inlet temperature of ammonia still is 40-50°C, and the temperature is increased up to 100°C inside the Still using steam.
Now, reference may be made to the following prior arts discussing state of the art techniques.
Several initiatives have been developed efficient removal of ammonia from the aqueous solution. United States Patent US4140586A provides that the thermal efficiency of an ammonia still is significantly increased by the use, in conjunction with the usual countercurrent steam stripping medium, of an auxiliary inert gas stripping medium initially heated and humidified by heat exchange with hot still bottoms derived from the still, i.e. preheated inert gas using waste heat has been used for enhanced ammonia removal.
Chinese Patent Application CN101259967 provides that generating vacuum improves the performance of still, more particularly it provides a manufacturing process for surplus ammonia water in the coal carbonization industry, wherein the surplus ammonia water is added in with sodium hydroxides in minute quantities and exchanges heat with waste water in a heat exchanger, and enters an ammonia still decompressed by a vacuum

pump, and the ammonia in the surplus ammonia water is volatilized in a negative pressure state, and the ammonia gases are cooled and sent to a next working procedure after being pressurized by the vacuum pump. The invention is characterized in that the surplus ammonia water is added in with sodium hydroxides so as to decompose and fix ammonium salts; the ammonia still is decompressed by the vacuum pump; the ammonia still is the material filling type ammonia still; and the waste water on the bottom of the ammonia still exchanges heat with the circulating ammonia water and returns to the ammonia still. The invention provides a new way for process technology of surplus ammonia water, and eliminates consumptions of resources such as steam and coal gas, etc. in the process of processing surplus ammonia water, thereby greatly lowering operating costs; moreover, the process of the invention has the advantages of low requirement of the process on the quality of fillers, low pre-stage investment and good economic benefits, and can be used in environments with low temperature and low pressure.
However, the prior art solutions are cost inclusive. Furthermore, there are several techniques to increase the temperature e.g., preheating using thermal or electrical energy. However, an appreciable operational cost is involved in such techniques.

SUMMARY
The present disclosure relates to a system (200) for thermal refining in ammonia still (208) using waste heat from battery liquor. The system (200) including a liquor storage tank (202) for storing the battery liquor; a buffer tank (204) coupled to the liquor storage tank (202); a gravel filter (206) coupled to the buffer tank (204); the ammonia still or distillation column (208) where the battery liquor is stripped of ammonia and cyanide, the distillation column (208) having a feed end (207) through which the battery liquor is fed to the distillation column (208) and a discharge end (209) through which treated battery liquor is discharged; a heat exchanger (210) coupled to the liquor storage tank (202), the feed end (207), and the discharged end (209), wherein the battery liquor is being configured to pass through the heat exchanger (210) to the distillation column (208); and a cooler (212), coupled to the heat exchanger (210), for receiving the treated battery liquor through the heat exchanger (210), in such a manner that heat of the treated battery liquor is transferred to the battery liquor coming from the battery liquor storage tank (202), thereby increasing the temperature of the battery liquor from the battery liquor storage tank (202) and decreasing the temperature of the treated battery liquor.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Further objects and advantages of this disclosure will be more apparent from the ensuing description when read in conjunction with the accompanying drawings of the exemplary embodiments and wherein:

Figure 1 shows: A schematic of a conventional ammonia still operation system 100.
Figure 2 shows: A schematic of a modified system 200 for thermal refining in ammonia still using waste heat according to an embodiment of the present disclosure.
The figure(s) depict embodiments of the present subject matter for the purposes of illustration only. A person skilled in the art will easily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.
DETAIL DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE PRESENT DISCLOSURE WITH REFERENCE TO THE ACCOMPANYING DRAWINGS
The present disclosure, now be described more specifically with reference to the following specification.
It should be noted that the description and figures merely illustrate the principles of the present subject matter. It should be appreciated by those skilled in the art that conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present subject matter. It should also

be appreciated by those skilled in the art that by devising various arrangements that, although not explicitly described or shown herein, embody the principles of the present subject matter and are included within its spirit and scope. Furthermore, all examples recited herein are principally intended expressly to be for pedagogical purposes to aid the reader in understanding the principles of the present subject matter and the concepts contributed by the inventor(s) to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. The novel features which are believed to be characteristic of the present subject matter, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures.
These and other advantages of the present subject matter would be described in greater detail with reference to the following figures. It should be noted that the description merely illustrates the principles of the present subject matter. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described herein, embody the principles of the present subject matter and are included within its scope.
Figure 1 illustrates schematic of a conventional ammonia still operation system 100. The system 100 includes a liquor storage tank 102, a buffer

tank 104, a gravel filter 106, a distillation column 108, and a cooler 110. The standard practice associated with the system 100 will now be explained in the foregoing description.
The distillation of excess flushing liquor or battery liquor (@40-50°C) involves feeding the liquor from the liquor storage tank 102 to the top of the distillation column 108, usually called Ammonia Still or still, and feeding a counter current flow of stripping steam (@100-102°C) at the bottom of the distillation column. Firstly, the liquor is pumped from the liquor storage tank 102 to the buffer tank 104, and then the liquor is fed to the still 108 through gravel filter 106 to remove tar particles. The steam distills off the ammonia and cyanide in the liquor, which leaves with the overhead vapours and passes on for further treatment. The treated liquor (@100- 102°C) is pumped from the bottom of the still 108, and is passed through a cooler 110 to achieve the temperature of the battery liquor below 40°C before discharge to Biological Oxygen Treatment (BOT) plant.
Typical levels of total ammonia in the liquor and in the treated liquor range from 100 to 150 ppm and 20 to 40 ppm. Further, not all the dissolved ammonia and cyanide present in excess flushing liquor is readily steam strippable. Many chemical species present in flushing liquor lead to the formation of various ammonium and cyanide salts in solution. These include ammonium carbonate, chloride, sulphate, cyanide and thio cyanate among others. Salts such as ammonium carbonate are easily decomposed by heat in

the still 108 to yield free molecules of ammonia. However, other salts such as ammonium chloride, sulphate, cyanide and thio cyanate are not decomposed and retain the ammonia and cyanide in a “fixed” form.
The fraction of fixed ammonia to total ammonia in the battery liquor is typically 20 to 50%. To allow the distillation of the fixed ammonia and cyanide, the excess flushing liquor must be made alkaline, for example by addition of sodium hydroxide (NaOH). The following typical reaction then takes place, liberating free molecules of ammonia:

Similarly, cyanide is also present in both ‘free’ and ‘fixed’ form in the battery liquor. ‘Free’ cyanide distilled off very easily by heating, however, to remove ‘fixed’ cyanide alkalisation is essential.
The addition of alkali is determined by mass balance, based on chemical analysis of the excess liquor to give the concentration of the fixed ammonia present. The generally ready availability and ease of handling of sodium hydroxide (caustic soda) NaOH solution has made it preferable for present day design of ammonia stills. However, caustic soda is the most expensive of the alkalis traditionally used, but its consumption can be closely controlled which is of great benefit where limitations are imposed upon still effluent pH. In practice, the caustic soda is injected into the ammonia still 108 near to,

but not at, the top tray. This allows dissolved acid gases such as hydrogen cyanide and hydrogen sulphide to be stripped from the liquor first, before they can react with the caustic soda to form fixed salts. The simple schematic has been shown in figure 1.
The treated battery liquor from the still 108 is passed through the cooler 110 to achieve the liquor temperature below 40°C for next subsequent biological oxygen treatment (BOT) process for further treatment of the treated battery liquor.
Figure 2 illustrates schematic of a modified system 200 for thermal refining in ammonia still using waste heat according to an embodiment of the present disclosure. The system 200 includes a liquor storage tank 202 for storing battery liquor, a buffer tank 204 coupled to the liquor storage tank 202, a gravel filter 206 coupled to the buffer tank 204, a distillation column 208 having a feed end 207 and a discharge end 209, a heat exchanger 210 coupled to the liquor storage tank 202, the feed end 207, and the discharged end 209, and a cooler 212 coupled to the heat exchanger 210. The modified practice associated with the system 200 will now be explained in the foregoing description, considering system 100 and the background of the process.
In operation, the battery liquor is stripped of ammonia and cyanide, the distillation column 208 having the feed end 207 through which the battery

liquor is fed to the distillation column 208 and the discharge end (209) through which treated battery liquor is discharged. Further, the battery liquor is being configured to pass through the heat exchanger 210 to the distillation column 208. Further, the cooler 212 is configured for receiving the treated battery liquor through the heat exchanger (210), in such a manner that heat of the treated battery liquor is transferred to the battery liquor coming from the battery liquor storage tank (202), thereby increasing the temperature of the battery liquor from the battery liquor storage tank (202) and decreasing the temperature of the treated battery liquor.
The main aim of process modification of ammonia still 208 of the system 200 is to enhance ammonia and cyanide removal efficiency as well as reduction of steam and caustic (NaOH) consumption during stripping. In an embodiment, the composition of the battery liquor is 7000-8000 ppm ammonia and 250-450 ppm cyanide. As discussed earlier, the pH of the battery liquor is around 9.5 to 10.5 and after distillation, it is around 8 to 8.5 though alkali is added during distillation. It has been analysed that battery liquor is in form of ‘buffer’ having pH 9.5 to 10.5. According to the principle of ‘buffer’, pH of the medium remains same for long period. Based on experimental study, with help of heating, ‘buffer’ of battery can be destroyed and as a result free ammonia as well as cyanide can be removed from battery liquor very easily. Therefore, consumption of alkali for free ammonia and cyanide will be minimized if the temperature of battery liquor is increased before alkali dosing and thus, preheating of battery liquor is

provided in accordance with an embodiment of the present disclosure in the system 200. The preheating of the battery liquor without any increment in operational cost of ammonia still and without major change in the whole process.
In an embodiment, the process 200 includes indirect heating using waste heat of treated battery liquor coming out from ammonia still 208. In an embodiment, the composition of the treated battery liquor is 50-100 ppm ammonia and 10-15 ppm cyanide. Such an operation is carried out by the heat exchanger 210. The heat exchanger (HE) is installed to transfer heat from treated liquor to feed liquor from the liquor storage tank 202. The temperature of the feed liquor is thereby increased up to 80°C from 45-50°C. As the temperature of the feed battery liquor is increased substantially, steam consumption for distillation as well as to maintain the constant temperature throughout the distillation column 208 is reduced. In an embodiment, the steam consumption for stripping ammonia from the battery liquor is reduced by 1.5 -2 ton/hr. The heat exchanger 208 has been designed according to existing process so that the operation is never hampered.
The thermal energy of the treated battery liquor is used to increase the temperature of the feed battery liquor through the heat exchanger 210 leading to the breakage of the “buffer solution” prior to the entry into the still 208. Moreover, the preheating of battery liquor has also ensured the

effective removal of dissolved acid gases such as hydrogen cyanide, hydrogen sulphide, etc. before it is exposed to alkali so that actual alkali consumption is reduced. Thus, the requirement of caustic has been drastically reduced. In an embodiment, the caustic consumption for stripping ammonia from the battery liquor is reduced by 30-35%. The system 200 not only increases the feed liquor temperature but also reduce the temperature of treated battery liquor. In an embodiment, temperature of the battery liquor is increased by 20-25°C, and the temperature of the treated battery liquor is reduced by 15-20°C. Thus, load of cooler also reduces up to 20-30% to achieve the temperature of treated liquor below 40°C.
Table 1, as provided in the foregoing description, shows quantified parameters associated with the system 200. The quantified parameters are evaluated over a period of time, for example six months.


It is evident from Table 1, that the system 200 as per the present disclosure leads to overall performance improvement of ammonia still by more than 30%.
It is to be noted that the present disclosure is susceptible to modifications, adaptations and changes by those skilled in the art. Such variant embodiments employing the concepts and features of this disclosure are intended to be within the scope of the present disclosure, which is further set forth under the following claims.

WE CLAIM :
1. An arrangement (200) for effective heat utilisation of a battery liquor, the arrangement (200) comprising:
a distillation column (208) where the battery liquor is stripped of
ammonia and cyanide;
the distillation column (208) having a feed end (207) through which
the battery liquor is fed to the distillation column (208) and a
discharge end (209) through which the battery liquor treated is
discharged;
both the feed end (207) and the discharged end (209) are being
coupled to a heat exchanger (210);
a battery liquor storage tank (202) configured to store the battery
liquor and being coupled to the heat exchanger (210), the battery
liquor being configured to pass through the heat exchanger (210) to
the distillation column (208); and a cooler (212) being coupled to the
heat exchanger (210) to which the battery liquor treated is being
received through the heat exchanger (210) in such a manner that h
eat of the battery liquor treated is transferred to the battery liquor
from the battery liquor storage tank (202) and increasing
temperature of the battery liquor from the battery liquor storage
tank (202) and decreasing the temperature of the battery liquor
treated.

2. The arrangement as claimed in claim 1, wherein the composition of the battery liquor is 7000-8000 ppm ammonia and 250-450 ppm cyanide.
3. The arrangement as claimed in claim 1, wherein the composition of the battery liquor treated is 50-100 ppm ammonia and 10-15 ppm cyanide.
4. The arrangement as claimed in claim 1, wherein the temperature of the battery liquor treated is reduced by 15-20oC.
5. The arrangement as claimed in claim 1, wherein the temperature of the battery liquor is increased by 20-25oC.
6. The arrangement as claimed in claim 1, wherein the steam consumption for stripping ammonia from the battery liquor is reduced by 1.5 -2 ton/hr.

7. The arrangement as claimed in claim 1, wherein the caustic consumption for stripping ammonia from the battery liquor is reduced by 30-35%.