Economizer with exhaust damper, fresh air damper, returan air damper and exhaust air damper. The dampers can be automaticlly controlled by PLC controller or by manual based on project needs.
This type HVAC system is another energy saving in the field of Air Conditioning.
Interlocked to run when return air dampers are being closed and supply air blower is in operation. The extraction fans run when outdoor air dampers are at least 50% open (adjustable). It is also overload protected. A gravity exhaust damper is supplied with this option to prevent air from entering the unit during shutdown.The power exhaust fans have been size to exhaust 50% of the nominal air flow of the unit.
The schematic diagram as below like free cooling system.
Rooftop Packaged Unit With Economizer Rooftop Packaged Unit With Economizer,Economizer HVAC Residential,Portable Rooftop with Economizer,Economizer Rooftop Packaged Unit Jinan Amrta Air Conditioning Co.,Ltd , https://www.waterchiller.pl
I. Overview
Jiangxi ion-adsorbed rare earth ore is mainly distributed in Longnan and Xunwu areas of the province. Geological exploration work has been identified: Longnan area is ion-adsorbing heavy rare earth ore; Xunwu area is ion-adsorbing light rare earth ore. Since 1971, seven mines have been built in Longnan and Xunwu areas, and mixed rare earths have been extracted and produced by chemical beneficiation . With the increase of the demand for medium and heavy rare earths at home and abroad, the rapid development of ion-adsorbed rare earth ore production has been promoted. At present, the annual output of rare earths extracted from Jiangxi ion-adsorbed rare earth ore has accounted for 15% to 20% of the total national rare earth production by oxide.
Second, the nature of the ore
The ion-adsorbed rare earth ore in Longnan and Xunwu areas of Jiangxi Province is formed by weathering of rare earth-bearing granite or volcanic rocks. The ore body is shallowly covered, the ore is loose, and the particles are very fine, which can be directly mined without blasting. The rare earth is mainly adsorbed on clay minerals such as kaolin in the form of ions, and the rare earth grade in the ore is 0.088% to 0.2%. This type of deposit has the following characteristics:
(1) 80%-90% of the rare earth elements in the ore belong to the ion-adsorbing phase, and a small part of the rare earth elements exist in the form of single mineral or similar minerals.
(2) Most rare earth elements are adsorbed on clay minerals such as kaolin in the form of ions. These clay minerals are mainly composed of halloysite, kaolin and hydromica .
(3) The rare earth cation adsorbed on the clay mineral is insoluble in water or ethanol, but ion exchange and entry can occur in a solution of a strong electrolyte such as NaCl, (NH 4 ) 2 SO 4 , NH 3 Cl, NH 4 AC, etc. The solution has a reversible reaction.
The above characteristics of the ion-adsorbed rare earth ore determine that the rare earth resources can be efficiently recovered from such ores by simple chemical beneficiation methods.
Third, the process and indicators
(a) sodium chloride method
The extraction of rare earth from ion-adsorbed ore by NaCl is one of the main chemical beneficiation methods for treating this type of ore. The ore transported from the stope is sent to a rectangular cement tank for immersion. The leaching solution is discharged from the discharge port through the filter layer at the bottom of the tank. The leaching residue is manually removed, and the leaching solution is precipitated in a saturated oxalic acid solution. After filtration, the filtrate is filtered through lime. The neutralized well is added with salt for reuse; the filter cake is rare earth oxalate, which is mixed with rare earth oxide by burning, washing with water and then burning. The chemical beneficiation process for treating ion-adsorbed rare earth ore with NaCl is shown in Fig. 1.
Fig.1 Chemical beneficiation process of ion-adsorbed rare earth ore by NaCl treatment
The main problem currently existing in this process is that the leaching residue contains high NaCl and causes soil salinization.
(2) Ammonium sulfate method
The extraction of rare earths from ion-adsorbed ores with (NH 4 ) 2 SO 4 is a successful method in recent years. The difference from the NaCl method is that the ore is immersed in a 1% to 2% (NH 4 ) 2 SO 4 solution, followed by precipitation with oxalic acid to obtain a rare earth oxalate, and after one burning, a REO>90% is obtained. The mixed rare earth oxide is used, and the filtrate is returned by adding ammonium sulfate. Compared with the NaCl method, the leaching residue does not cause soil salinization problems. The chemical beneficiation process for treating ion-adsorbed rare earth ore with (NH 4 ) 2 SO 4 is shown in Fig. 2.
Fig. 2 Chemical beneficiation process for treatment of ion-adsorbed rare earth ore with (NH 4 ) 2 SO 4
(3) Production indicators
The production indicators of Longnan and Xunwu Mines in 1981 are listed in Table 1. It can be seen from the listed indicators that the production indexes of these two mines are still relatively low, and the total recovery rate of rare earths is only 60%-65%. Therefore, reasonable chemical beneficiation process and mining and selection equipment have yet to be further developed.
Table 1 Production index of Jiangxi ion-adsorbed rare earth ore in 1981
Project
Longnan (heavy rare earth) mine
Project
Xunwu (light rare earth) mine
Medium and small mines
Large mine
Leach rate, %
81.08
89.78
Leach rate, %
80～89
Extraction rare earth yield, %
95
Burning water washing yield, %
70.00
72.00
Extraction group yield, %
94
Precipitation burning yield, %
94
Total rare earth yield, %
52~56
59.47
Total rare earth yield, %
65