Synthetic Ammonia Weekly Topic 12/19--12/26: How to handle ammonia and methanol in process condensates
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Weekly topic on ammonia synthesis: How to handle ammonia and methanol in the process condensate. During the operation of ammonia synthesis plants, the secondary furnace can produce a small amount of ammonia, while the low-temperature converter can generate a small amount of methanol; these substances, along with some of the CO2 present in the feed gas, end up in the condensate. Question: How to handle ammonia and methanol in process condensate? Generally, the stripping method is used to separate it from the condensate. What is done with it after separation? Everyone is welcome to participate actively in the discussions; those who do so will receive a wealth reward of at least 10 points. Thank you to all participants.
Some manufacturers send water to the gas generation jacket after gas treatment to produce steam, or via biochemical terminal treatment. We have also conducted experiments showing that by heating the transformed condensate and then subjecting it to air stripping, COD and ammonia nitrogen levels can be reduced to a level sufficient for biochemical treatment.
This post was last edited by rzs20000 on 2011-12-18 at 20:43. After the process condensate is stripped using low-pressure steam, although the wastewater meets the environmental discharge standards, it still results in a waste of water resources. Moreover, fees have to be paid to environmental authorities for discharging such wastewater. To save water resources and achieve zero discharge, measures need to be taken. Given that the COD in the wastewater is primarily composed of methanol, it is necessary to degrade the methanol in the wastewater using biochemical methods before it can be treated with ion exchange resins to enable water recovery. The specific plan is as follows: The wastewater discharged from the condensate stripping unit in the methanol-containing process passes through a set of bioreactors and an ozone treatment system to meet the requirements for boiler feedwater. The new equipment includes biological ceramsite reactors, ultrafiltration units, ozone oxidation reactors, activated carbon adsorption units, and ion exchange systems. Each of these components is described as follows: Biological Ceramsite Reactors: There are two such reactors; the ceramsite biological reactors consume methanol, and the water produced flows naturally into a water tank ； After the biological ceramsite reactor has been in operation for a period of time, it is necessary to subject the ceramsites to air impact to prevent caking of the ceramsites within the reactor. Ultrafiltration unit: Due to the large amount of bacteria and their metabolic products present in the biochemical reactor, ultrafiltration can achieve optimal removal of organic substances, thereby reducing the workload on the subsequent superoxidation stage. Water moves in a cross-flow pattern across the membrane surface: one part of the water passes through the membrane to become the product water, while another part flows over the surface of the membrane, carrying away any impurities that have accumulated there. This water exits the membrane module and can be used as return flow, entering the inlet of the biological ceramsite reactor. After the system has been operating for a certain period of time, some suspended particles and colloids may adhere to the membrane surface, affecting its performance; in such cases, air-water backwashing of the membrane elements is necessary to restore their operational efficiency. Ozone oxidation reactor: The product water coming out of the microfiltration membrane enters the ozone oxidation reactor. The water flows from top to bottom, while ozone is introduced from below through a microporous generator to oxidize the incoming water, converting the organic substances that have passed through the microfiltration membrane into organic acids ； To increase the oxidation conversion rate, the pH value of the incoming water is raised to 9.5–10, and the effluent naturally overflows into a water tank. Activated carbon adsorption unit: The water treated by the ozone reactor is rich in ozone, which can cause some damage to the ion exchange resin; this ozone is removed through activation carbon adsorption. Organic acids that have been oxidized with ozone are exchanged using strong alkaline anion exchange resins with a low degree of cross-linking, which are capable of resisting organic pollution; as a result, the effluent can meet the requirement of less than 1 ppm. It meets the requirements for boiler feedwater and is entirely recovered as boiler feedwater.
Our process involves stripping the process condensate with low-pressure steam, and the non-condensable gases such as methanol and CO2 that are separated are released directly into the atmosphere. This results in an evacuation rate of about 1.1 T per hour, leading to energy waste and air pollution, which is quite unfortunate. The condensed liquid after stripping, as long as its conductivity is within acceptable limits, is sent to the utility demineralized water unit for further treatment. Unqualified; discharge on-site and investigate the cause.
Some use heat exchange for purification and separation, while others employ ion exchange membranes for separation; after separation, the product is sent to specialized storage tanks for reuse
A low-pressure stripping recovery method for the condensate in the ammonia synthesis process, wherein the condensate is fed into a low-pressure stripping tower and brought into countercurrent contact with low-pressure steam, thereby stripping out NH3, CO2, CODcr, and methanol from the solution； It then passes through the urea condensate preheater, the desalinated water preheater, and the circulating water cooler in sequence, before entering the activated carbon filter; after being processed by the desalinated water treatment system, it is used as boiler water ； The stripping saturated steam drawn from the stripper loses heat in the carbon dioxide recovery reboiler before entering the non-condensable gas separator. The non-condensable gas is washed with deionized water and then sent to the first-stage furnace, where it is mixed with natural gas and burned ； The condensate returns to the urea condensate storage tank, where it mixes with the urea condensate before being recycled through the pipes. This method reduces the load on the clarifier tank, lowers the costs associated with the raw materials used in treatment, recovers dissolved natural gas, reduces the emission of various harmful substances in the condensate, improves environmental conditions, and offers good economic benefits as well as significant social benefits.
The condensate is stripped, and once the liquid meets the required standards it is sent to other processes for further use. The gas, on the other hand, must first be cooled to a certain temperature before being discharged into the flare system, which represents some waste.
Ammonia in the condensate can be removed using low-pressure steam stripping; methanol removal is accomplished through biological ceramsite reactors, in combination with ultrafiltration units and activated carbon adsorption, as well as various microbial methods
Our process is the same as what the original poster mentioned, but the desalination station cannot be treated with resin; moss grows on the resin within two or three days, causing severe damage to it. I started preparing to add an activated carbon filter, but after careful consideration, the pipeline was ultimately sent to the fire tank as raw water.
After being stripped with medium-pressure steam, the process condensate has a conductivity of less than 50 us/cm and is sent to the utility system. Ammonia and methanol are sent to the first-stage furnace for reaction along with the medium-pressure steam.
We did not treat the condensate; instead, we discharged it directly into the circulation tank as make-up water.