Cause analysis and treatment of the low pH value o

Cause analysis and treatment of low pH value of boiler water

large ammonia plants have many characteristics, one of which is that they all have a complete set of heat recovery system. Make full use of the waste heat in the process to produce high-pressure steam, which not only provides the power required by various rotating equipment, but also can be used as process steam and heating medium, so as to greatly reduce the external power supply consumption, greatly reduce the cost, and can be less affected by the external power supply

in order to ensure steam quality and prevent equipment corrosion, the boiler of high-pressure steam generation system has high and very strict requirements for its water quality, in which the pH value of boiler water is one of the indicators to be strictly controlled, although at present, when the pH value of boiler water is greater than 11, alkaline corrosion will be caused. However, the pH value of boiler water should not be lower than 9. First, when the pH value is low, the corrosion of water to boiler steel increases; Second, the boiler only uses the speed characteristics of the stepper motor itself. Only when the pH value of water is high enough, the acid radicals in the water and metal ions form water slag that is easy to be eliminated; Third, it is to inhibit the hydrolysis of silicate in boiler water and reduce the dissolved carrying amount of silicate in steam

the pH value of boiler water in our plant is adjusted by adding p-nitrohexane (morpholine) to the feed water. When the pH value is high, the dosage can be reduced. However, the phenomenon that the pH value of feedwater is normal (greater than 9) and the pH value of boiler water is low has occurred in operation. Now, the reasons for the low pH value of boiler water are analyzed

2 reasons for low pH value of boiler water

under the condition of normal operation of the unit and normal pH value of feedwater, the pH value of boiler water should not have decreased due to concentration of boiler feedwater. So what is the reason for the low pH value of boiler water? Through observation, it is found that the low pH value of boiler water is phased, mostly in spring and summer. We analyzed many aspects and tested the raw water. It was found that there were trace organic acids in the Yellow River water. After adding test pieces in the water, the workshop could not remove these organic acids. They entered the drum with the feed water. After concentration, the organic acids accumulated in the boiler water, resulting in the low pH value of the boiler water

in addition, sometimes there is a small amount of organic acid in the drugs due to the unsatisfactory quality of the drugs added, which will also lead to the low pH value of the boiler water

3 treatment when the pH value of boiler water is low

when the pH value of boiler water is low, the cause should be found out in time, and those that can be controlled by the system should be treated in time (for example, qualified drugs should be purchased for drug problems), and those that cannot be controlled (for example, the Yellow River water problem) should be remedied by strengthening sewage discharge

the blowdown of steam drum can be divided into two forms: intermittent blowdown and continuous blowdown. Intermittent blowdown is located at the bottom of the drum. Its task is to discharge the slag and sundries deposited at the bottom of the drum, which has a certain effect on the discharge of organic acids. However, normal blowdown mainly depends on continuous blowdown, which is the continuous discharge of some boiler water from the drum, and the discharge of fine or suspended slag and organic matter in the boiler water. The continuous blowdown water intake is located in the middle of the drum, generally about 10cm below the normal liquid level and near the bottom of the cyclone separator, because this is the place where impurities, suspended solids and organic matter are concentrated. Therefore, the control of drum liquid level is very important. If the drum liquid level is too high, the suspended solids, impurities and organic matter cannot be discharged in sufficient quantity, resulting in accumulation. If the sewage discharge is increased, not only the fuel consumption will be increased, but also a large amount of boiler feed water will be discharged, causing unnecessary losses; If the liquid level is controlled too low, some steam will inevitably be discharged from the blowdown pipe, which will not only fail to achieve the purpose of blowdown, but also cause waste

4 conclusion

when the pH value of boiler water is low and within an appropriate range, find out the cause, do a good job in drum level control, and adhere to 12.7mm wide intermittent blowdown every shift according to the adjustment of continuous blowdown volume. The problem of low pH value of boiler water can be solved