Technical Discussion: Methods and Approaches for Treating Wastewater Containing Ammonia Nitrogen

This post was last edited by hesonchang214 on 2009-8-20 at 10:38. The process of supporting the gas membrane (also known as membrane-driven desorption-chemical absorption, which is equivalent to combining two towers – a stripping tower and an acid absorption tower – on a microscopic level): Hydrophobic microporous hollow fiber membranes are used; an aqueous solution of ammonia (or volatile amines) flows on one side of the membrane, while dilute sulfuric acid, dilute hydrochloric acid, or dilute phosphoric acid flows on the other side. The highly volatile ammonia (or volatile amines) pass through the gas membrane and are irreversibly chemically absorbed into the acid solution, thereby enabling their removal, recovery, purification, and enrichment. Advantages: It is extremely effective and suitable for the recovery of ammonia (or volatile amines) at low or very low concentrations (500 – 10,000 ppm), thereby enabling the wastewater to meet discharge standards or be reused. No heating, pressurization, or vacuum operation is required; the ammonia or amines in the wastewater can be concentrated by dozens to hundreds of times, with their concentration reduced to 15 or even less than 1 ppm. Disadvantage: The pH value needs to be adjusted to 11–12 in advance. The by-product obtained is an ammonium salt; if ammonia (or amine) is to be reused, alkali (sodium hydroxide or calcium hydroxide) must be added, followed by processes such as distillation to obtain a high-concentration ammonia (or amine) solution. Wastewater requirements: The pre-treated wastewater must be free of suspended solids, oils, surfactants, oxidants, etc. We provide ready-made equipment. The micropores on the walls of our hollow fiber membranes are circular holes with a diameter of 0.02 micrometers, which gives them better operational stability compared to the flat-pore membranes produced by the stretching method currently used in China (with dimensions of 0.2x0.02 micrometers).

Hehe, I have done research on this area; we can collaborate!

This post was last edited by hesonchang214 on 2009-8-20 10:53. Treatment solutions for chemical wastewater containing ammonia and nitrogen • Introduction: This article presents a treatment plan for wastewater containing ammonia and nitrogen from a chemical plant. First, the design scope and standard requirements are established based on the project overview; thereafter, the use of an ammonia vaporization tower is decided upon. The construction methods, process flow, and characteristics of this approach are then described. • Keywords: wastewater containing ammonia nitrogen, wastewater treatment, wastewater treatment solutions, ammonia evaporation tower. Overview: XX Coking Plant is a newly built large-scale coking plant in China, with a designed capacity of 400,000 tons of coke per year, along with corresponding chemical production facilities. For a coking plant with a capacity of 400,000 tons per year, the amount of excess ammonia water generated is approximately 10 tons per hour. The remaining ammonia wastewater treatment process involves direct steam ammonia evaporation; the resulting concentrated ammonia vapor is sent to the desulfurization unit for reuse, while the wastewater after ammonia evaporation is cooled before being sent to the biological treatment station. Design content: The ammonia distillation system for residual ammonia water described in the plan is considered as a new project. The remaining ammonia water is subjected to distillation to meet the requirements for biochemical treatment (or to be reused in coke quenching). The ammonia vapor obtained from distillation is mixed with cold drum gas and sent to an ammonium sulfate saturator for recovery, thereby preventing secondary pollution. Therefore, this system must operate in conjunction with the ammonium sulfate production system. Construction scale, designed influent quality of residual ammonia water, and emission standards to be achieved. The ammonia vaporization system is designed for a flow rate of 10 m3/h, which corresponds to the amount of residual ammonia water generated by a coking plant producing 400,000 tons of coke per year. The ammonia vaporization system is used only to treat the remaining ammonia water. This remaining ammonia water is designed to have an NH3-N concentration of up to 3500 mg/L; the NH3-N concentration in the wastewater after treatment (i.e., volatile ammonia) is required to be less than 200 mg/L in order to meet the requirements for subsequent reuse in coke quenching processes. Determination of the scheme I. Ammonia evaporation tower scheme In the early days of the coking industry, cast iron grating towers or bubble towers were commonly used for ammonia evaporation. Due to their low processing efficiency and numerous problems, these systems could not operate properly; it was often difficult to keep the NH3-N concentration in the wastewater at low levels, which made it impossible to meet the requirements for reusing the water in quenching processes. This plan adopts the stainless steel guided floating valve column independently developed by our company as the main distillation equipment. With a guided floating valve tower, oil contamination does not accumulate easily, and operation and maintenance are simple. The ammonia vapor generated through evaporation is used for desulfurization or recovered via an ammonium sulfate system, resulting in no secondary pollution. The guided floating valve ammonia distillation tower is introduced as follows: 1.) Overview: The ammonia distillation tower is the core equipment in the ammonia distillation process. The guided floating valve ammonia distillation tower is a distillation device developed independently by our company and represents an advanced technology in China. It can be widely used in industries such as coking, fertilizer production, gasification, chemicals, and biological fermentation for distillation and separation purposes. It features high efficiency, great operational flexibility, a long equipment maintenance cycle, and a long service life. It is particularly suitable for the distillation treatment of ammonia-containing wastewater, and has been successfully applied in numerous projects. 　2.) Principle: In a guided floating valve distillation tower used for treating ammonia-containing wastewater, in order to ensure the stable operation of the system, a small amount of caustic soda is added to the remaining ammonia solution before it enters the ammonia vaporization tower, in order to adjust the pH value to the desired level. After preheating, the solution enters the tower from the top, while saturated steam is introduced from the bottom. The vapor and liquid come into contact with each other in counterflow across the tray layers, thereby facilitating heat exchange and mass transfer. Due to ammonia’s higher volatility compared to water, it continuously transfers from the liquid phase to the vapor phase, where it is concentrated and separated in the top condenser for reuse. The ammonia concentration in the wastewater decreases gradually as it moves downward through the tower; by the time it reaches the bottom of the tower, its concentration is ≤200 mg/L (the ammonia concentration at the inlet is around 2500 mg/L), which meets the requirements of the process design and satisfies the conditions for reuse. 　　 3.) Features: (1) The guided floating valve tray is one of the best trays available in China at present. Guided floating valve trays possess excellent hydrodynamic and mass transfer properties. They retain the advantages of conventional floating valve trays while overcoming their shortcomings. Compared with F1 floating valves, they offer a processing capacity that is about 20% higher, an efficiency increase of 10–20%, and a reduced tray pressure drop of around 20%. ⑵The guiding float valve tray is equipped with one or two guiding holes, the opening direction of which is aligned with the flow direction of the liquid on the tray. During operation, a small amount of gas ejected from these guiding holes drives the liquid on the tray to move, thereby significantly reducing or even eliminating the liquid level gradient on the tray. It also eliminates areas where liquid stagnates on the tray and reduces liquid leakage. ⑶The guide floating valve is rectangular; during operation, gas is primarily ejected from both sides of the floating valve, and the direction of gas ejection is perpendicular to the direction of the liquid flow. As a result, liquid backmixing on the tray is minimal, which contributes to its high efficiency. ⑷The valve body does not rotate during operation, so it experiences little wear, is not prone to falling off, and has a long service life. ⑸The tray itself is not prone to clogging, has a long operational life, requires minimal maintenance, and can **reduce repair costs**. ⑹The main material of the ammonia vaporization tower is stainless steel, which offers good corrosion resistance; any residual sludge or scale can be easily removed. The equipment has a long service life. Compared to cast-iron bubble towers and cast-iron grating towers, it handles larger volumes of material, provides greater operational flexibility, is easier to maintain, is lightweight, does not require a framework, and results in lower civil engineering costs. 　　 4.) Operating instructions for the ammonia vaporization tower: ⑴ The operating pressure, temperature, and wastewater flow rate of the tower must be strictly maintained within the design parameters – the pressure should be ≤0.04 Mpa, the temperature at the bottom of the tower should be ≤110°C, and the flow rate should be within 10 tons per hour. ⑵The liquid level of the wastewater at the bottom of the tower should be kept within the range that can be displayed by the level gauge, to prevent the tower from being emptied, steam from escaping from the bottom, or the tower from becoming flooded, which could affect its operational efficiency. ⑶Pay regular attention to the pressure drop within the tower; a high pressure drop indicates blockage inside the tower, and appropriate measures should be taken to promptly clean the trays or the blocked pipe openings. ⑷The control of the tower should take into account factors such as the top temperature and bottom temperature of the tower, the top pressure and bottom pressure, as well as the pH and flow rate of the residual ammonia water fed into the tower. (5) A safety valve and a check valve should be installed at the ammonia vapor outlet of the tower top condenser to prevent backflow of gas and avoid accidents. 　　 II. Reducer Scheme The reducer utilizes the 4-pass U-tube heat exchanger, which was developed and applied by our company earliest; the main material of this heat exchanger is 304. One end of the heat exchanger is inserted directly into the top of the ammonia vaporization tower. Ammonia vapor flows through the shell side, where baffle plates are present, while cooling water flows inside the U-tubes. Due to its high efficiency, its designed heat exchange area is 24 square meters. 　III. pH Regulation System Since the pH of the incoming ammonia water is unstable, in order to ensure the stable operation of the entire ammonia evaporation system and achieve consistent treatment results, a pH regulation system is necessary. This system consists of an alkali storage tank, an alkali solution metering pump, and an automatic control system. 　　 IV. Options for the heat source in distillation: Use low-pressure steam at 0.3–0.6 MPa to directly supply heat to the ammonia distillation tower. V. Brief description of the process flow The key equipment in the ammonia vaporization system is the ammonia vaporization tower; our company has developed an advanced guide float valve tower of domestic standard, which ensures a high degree of operational flexibility. Even when the amount of residual ammonia water and its concentration change, the wastewater can still be treated effectively, and the steam flow rate can be adjusted based on the total amount of ammonia water vapor recovered to reduce consumption. 　The remaining ammonia water is pressurized by an ammonia water pump and sent to a filter. At the outlet of the ammonia water pump, a branch pipe is taken off, and an alkaline solution is added to the remaining ammonia water using a metering pump. The ammonia water with the added alkali is mixed evenly in a static mixer to adjust the pH value. Particulates that can cause scale formation are removed by the filter, while oils such as tar are adsorbed away. Afterwards, it enters a heat exchanger where it exchanges heat with the distilled hot wastewater; the preheated remaining ammonia water then goes into the ammonia vaporization tower. The heat source required for distillation can be direct steam or heat transfer oil. Direct steam is added at the bottom of the tower and comes into counter-current contact with the liquid; the ammonia vapor generated is sent to the desulfurization unit or to the gas pipeline before the ammonium sulfate saturator for ammonia recovery. The wastewater resulting from distillation at the bottom of the tower is cooled to around 60°C through heat exchange with ammonia water fed into the tower, thereby enabling full recovery of waste heat; it is then cooled to 40°C before being sent to the biochemical treatment facility. 　　In summary, the distillation method for recovering ammonia from residual ammonia water is simple and reliable, ensuring effective ammonia removal from wastewater ； With a guided floating valve tower, oil residues do not accumulate easily, and operation and maintenance are simple ； The ammonia vapor distilled off is used for desulfurization or fed into the ammonium sulfate recovery system, thereby avoiding secondary pollution. VI. Process characteristics: (1) To control the NH3-N level in wastewater, adding NaOH before distillation enables the entire system to operate stably, ensures the recovery of ammonia, does not affect the quality of ammonium sulfate, and allows the NH3-N level in the treated wastewater to be kept at a low level. 　(2) An advanced guide floating valve tower developed by our company is used as the ammonia vaporization tower, meeting the requirements for a high degree of operational flexibility; heavy oil residues and other solid substances do not tend to accumulate inside the tower. 　(3) The sulfur-ammonia system using gas production simplifies the treatment steps and saves on investment. 　(4) Utilizing coke oven gas for combustion heating and heat transfer oil to heat wastewater directly to generate steam – this approach is innovative, and there is existing proven experience in its use. It makes full use of waste heat to reduce energy consumption, lowers the demand for direct steam and thereby reduces wastewater generation, lessens the burden on biological treatment processes, and cuts down on capital investment. VII. List of Main Equipment
(1) Ammonia evaporation tower: 1 unit, made of stainless steel.
(2) Thinner: 1 unit, made of stainless steel.
(3) Filter: 1 unit, made of carbon steel; one in use and one as backup.
(4) Wastewater heat exchangers: 2 units.
(5) Alkali storage tank: 1 unit, made of carbon steel (equipped with a level gauge).
(6) Metering pump: 1 unit.
(7) Ammonia water pumps: 2 units.
(8) Wastewater pumps: 2 units.
(9) Wastewater cooler: 1 unit.
(10) Wastewater tank: 1 unit.
(11) Static mixer: 1 unit, made of carbon steel.
(12) Electrical and instrumentation equipment: 1 set.

VIII. Utility and Auxiliary Systems
1. Water supply: It can follow the original design; the amount of circulating cooling water required for the ammonia evaporation system can be calculated at 120 m3/h. The circulating cooling water can be sourced from the plant’s circulating water system, with the return water temperature from this system ranging from 40 to 45°C. This water is then returned to the circulating water return pipeline. 2.) Steam: If direct steam is used as the heat source for distillation, the steam consumption for the ammonia evaporation system is 2 t/h, and low-pressure steam at 0.3–0.6 MPa can be utilized. If heat transfer oil is used as the heat source, no direct steam is consumed. 3.) If heat transfer oil is used as the heating source for distilling coke oven gas, the consumption of coke oven gas in the heat transfer oil heater (with a calorific value of 4000 kcal/Nm3) is 320 Nm3/h. 4.) Testing: The analysis tasks involved in this project mainly include the NH3-N concentration and pH levels of the materials entering and leaving the system. No special testing requirements exist; the analysis work can be carried out by the personnel responsible for analyzing the production processes and products in the coking plant, as well as by their laboratory, without the need for additional setup. 5.) Maintenance: The mechanical, electrical, and instrumentation maintenance of the production units in this project shall, in principle, be carried out by the existing staff at the coking plant, with no new maintenance personnel to be hired. IX. Working System and Staffing The production units, auxiliary equipment, and utility facilities operate at 8640 hours per year, with three shifts per day; four shifts of operators are assigned, resulting in a four-shifts-three-operational Pattern. X. Technical Economics 1.) Construction scale and product plan: The ammonia vaporization system is designed to treat approximately 864,000 tons of residual ammonia water per year. Product plan: Recover 1,296 tons per year of ammonia vapor containing 20% (NH3) (based on an NH3-N concentration of 3,000 mg/l in the wastewater), which corresponds to the production of approximately 2,013 tons per year of ammonium sulfate. Some light and heavy oils were also recovered (related to the tar content in the wastewater). 2.) Estimation of operating costs: Alkali solution: 2 yuan/kg × 50 kg/h ÷ 50 t/h = 2 yuan per ton of wastewater. Electricity cost: 0.5 yuan/kWh × 15 kW ÷ 50 t/h = 0.15 yuan per ton of wastewater. Labor cost: 800 yuan/person-month × 4 people ÷ (50 t/h × 24 × 30) = 0.09 yuan per ton of wastewater. Circulating cooling water cost: 0.2 yuan/t × 120 t/h ÷ 50 t/h = 0.48 yuan per ton of wastewater. Steam cost: 100 yuan/t × ** t/h ÷ 50 t/h = 15 yuan per ton of wastewater. Total operating cost: 17.72 yuan per ton of wastewater. This is for reference only. Feel free to contact us for further discussion. ***This solution has been put into practical use with good results; it has been supplied to over 20 companies in the past two years. Based on feedback from users, they are very satisfied with it***

OP, how high is the ammonia nitrogen wastewater concentration you are referring to? Different concentrations require different treatment methods. If the concentration is high, a distillation unit can be considered to recover ammonia nitrogen ； If the concentration is low, only biochemical treatment can be used.

This post was last edited by hesonchang214 on 2009-8-20 11:01 via acidic water stripping.

Our ammonia nitrogen water treatment uses evaporation concentration + membrane separation technology.

This post was last edited by hesonchang214 on 2009-8-20 at 11:01. Our company uses membrane treatment and evaporation concentration.

This post was last edited by hesonchang214 on 2009-8-20 at 11:02. It should be membrane separation technology (reverse osmosis) + (multi-effect) evaporation concentration.

This post was last edited by hesonchang214 on 2009-8-20 10:59. Membrane treatment: Reverse osmosis or electrodialysis? If reverse osmosis is used to concentrate an ammonium chloride aqueous solution to 6%, approximately 70 atm is required; for higher concentrations, multi-effect evaporation plus crystallization is necessary. Suitable wastewater: It contains very few impurities in water, no suspended solids, no emulsified oil droplets, and no significant amounts of organic solvents. More importantly, it must not contain any other salt ions; otherwise, only mixed salts will be obtained, which cannot be used as fertilizer. In the case where both sodium ions and ammonia (ammonium ions) are present, it is still more economical to use a support gas membrane (membrane desorption-chemical absorption). Furthermore, industrial evaporators are generally 2 to 6 effect, with a water production ratio of less than 4; therefore, treating one ton of an aqueous solution containing 6% ammonium chloride requires 0.25 to 0.5 tons of steam at around 150 degrees Celsius. The cost of steam for treating one ton of concentrated brine is 35 to 70 yuan ； If membrane-based multi-stage multi-effect evaporation is used instead, the water production ratio is 6–8. However, it requires steam at 100 degrees Celsius; the cost of steam for treating one ton of brine is 10–20 yuan.

A stripping tower and an acid absorption tower represent the most cost-effective approach; the membrane separation and floating valve tower methods mentioned above require higher initial equipment investments.