The main component of potassium humate is aromatic hydroxycarboxylate; Potassium fulvate is mainly composed of short carbon chain molecular structure substances. Source difference: potassium humate is extracted by KOH liquid reaction after fine separation of lignite. Potassium fulvic acid is extracted from natural humic acid. Application difference: potassium humate is mainly used in petroleum, chemical industry and building materials. Potassium fulvate is used in agriculture and horticulture.
Fulvic acid is a component of humic acid. Humic acid widely exists in peat, lignite, weathered coal, etc. from humic acid, a certain amount of fulvic acid and potassium oxide can be extracted to make potassium fulvate.
Potassium fulvate is black, and the solution has a certain viscosity. The traditional production process enters the subsequent drying system after evaporation and concentration. Generally, there are spray granulation drying and drum scraper drying. The feed concentration of spray granulation drying cannot be too high. The traditional evaporation process for the production of potassium fulvate generally adopts a reaction kettle for preliminary evaporation and concentration. The operation of the reaction kettle is simple, but the energy consumption is too high, and intermittent unloading, and the production continuity is poor. With the continuous rise of national energy prices, using the traditional evaporation process can no longer meet the current national requirements for energy conservation and emission reduction. A more energy-saving multi effect /mvr evaporation process can be used to integrate the solution characteristics of potassium fulvate, The evaporator adopts the form of forced circulation of tubes.
Potassium fulvate solution is alkaline and has high viscosity. Especially with the increase of concentration, the viscosity of the solution increases significantly. Generally, the feed concentration is about 20%. After the solution boils, it has strong foaming property, and foam seriously affects the evaporation operation. The process design considers to configure demisting device, and equipped with defoamer dosing system to reduce foam, prevent material runout, and ensure the stable operation of the system. The content of calcium and magnesium in potassium fulvate solution is high, but they all exist in the form of chelates, The evaporator design needs to be equipped with a chemical cleaning device for regular chemical cleaning. The temperature rise of the boiling point of the solution is not high. The evaporation can be in the form of multi effect /mvr. MVR process is preferred, which is more energy-saving.
①Multi effect evaporation process
Multi effect evaporation is a series evaporation operation that takes the secondary steam of the former effect as the heating steam of the next effect. In multi effect evaporation, the operating pressure of each effect, the corresponding heating steam temperature and the boiling point of the solution decrease in turn. Principle in evaporation production, the output of secondary steam is large and contains a large amount of latent heat, so it should be recycled to achieve energy-saving effect. Generally, the consumption per ton of evaporated steam is: single effect: 1.1t/ ton of water, secondary effect: 0.57t/ ton of water, third effect: 0.4t/ ton of water, and fourth effect: 0.3t/ ton of water.
Material flow direction:
Raw material tank → preheater → 1 Effect → 3 Effect → 2 Effect → concentrated liquid (mixed flow evaporation to ensure high temperature discharge)
Steam flow direction:
Steam → heat pump (steam ejected by the first effect separator) → 1-effect heater → 2-effect heater → 3-effect heater → main condenser
Condensate flow direction: 1-effect heater → condensate tank → condensate pump → preheater → reuse / discharge
Flow direction of distilled water: 2-effect heater → 3-effect heater / main condenser → distilled water tank → distilled water pump → reuse / discharge
In the evaporation process, the key operating indicators (liquid level, temperature, pressure, density, etc.) are automatically controlled by the automatic control system. The pressure of the evaporation tank and crystallizer is maintained at a certain pressure, and the evaporation pressure is adjusted and controlled by the bypass air regulating valve at the non condensable gas outlet of the distilled water tank.
In the forced circulation evaporation and concentration system, the discharge concentration of the concentrated liquid is detected by the mass flowmeter installed in the discharge pipeline, and the discharge is controlled by the discharge pump and the discharge regulating valve.
② MVR evaporation process
The working process of MVR is to compress the low-grade steam through the compressor, increase the temperature and pressure, increase the enthalpy, and then enter the heat exchanger for condensation, so as to make full use of the latent heat of steam. Except for start-up, there is no need to generate steam in the whole evaporation process. The secondary steam from the separator is compressed by the compressor, the pressure and temperature rise, and the enthalpy increase, and then sent to the heating chamber of the evaporator as heating steam to maintain the boiling state of the feed liquid, while the heating steam itself condenses into water. In this way, the steam originally to be discarded can be fully utilized, the latent heat can be recovered, the thermal efficiency can be improved, and the energy consumption per ton of water evaporated by MVR is about 28~55 yuan.
Material flow direction:
Raw water tank → feed pump → preheater → MVR forced circulation evaporation system → discharge pump → concentrated liquid
Steam flow direction:
Separator secondary steam → steam compressor → heater
The evaporation system adopts the forced circulation process and is equipped with a forced circulation pump to ensure the high-speed flow of materials in the full pipe in the row and prevent the materials from scaling and blocking the pipe. The characteristics of forced circulation process are as follows:
A. forced circulation evaporator is used to avoid scaling or crystallization caused by boiling on the heating surface.
B. forced circulation evaporation solution circulation in the equipment mainly depends on the circulation pump to generate forced flow.
C. the material will not evaporate in the heater, and the concentration will not change. The concentration will increase only after flashing in the separator, so it will not adhere to the heat exchange surface and cause scaling on the heat exchange surface.
D. the separation main body has a very sufficient liquid / gas separation area and separation height, which can ensure the stability of long-term evaporation and discharge concentration.
Considering the high salt content of the material feed, when the evaporation concentration reaches the end point, the system is equipped with a mass flowmeter to detect the density of the material, and is equipped with a discharge pump and a discharge regulating valve to regulate the discharge concentration by regulating the opening of the regulating valve.