Application of Loose Flange in Aerospace Pulverized Coal Gasification Plant

The application of lap joint flanges on equipment, special fittings and metal hoses in aerospace pulverized coal gasification plants is introduced, and it is determined that butt-weld ring lap joint flange should be used in the above occasions according to relevant specifications. This paper has a certain reference significance for the selection of loose flanges in similar occasions.

What is a loose flange?

Loose flange (LJ flange) is the use of a stub end or steel ring to cover the flange on the pipe end, the flange can be freely rotated on the end of the pipe, see Figure 1. at present, loose flange in non-metallic lined pipeline is widely used, the use of loose flange can make the construction, installation and subsequent replacement of the pipeline more convenient, while saving time for the successful completion of the project.

Figure.1 Diagram of lap joint flange
Aisino pulverized coal gasification process adopts inert gas to transport coal, and uses pure oxygen and water vapor as gasification agent to gasify pulverized coal at a pressure of 4.0 MPa G and temperature of 1200-1700℃, and adopts a radical cooling process to produce crude synthesis gas. The aerospace pulverized coal gasification plant mainly includes coal grinding and drying unit, coal pressurization and coal feeding unit, gasification and syngas scrubbing unit, and slag and grey water treatment unit.
In the aerospace pulverized coal gasification plant, considering the construction or maintenance convenience, will also use the loose flange, the following summary of its application.

1. Application of loose flange on the equipment

Figure.2 Application of lap joint flange on the equipment
In the gasification and syngas scrubbing unit of the aerospace pulverized coal gasification plant, the opening ejector and the ejector separator tank are directly connected through the flange orifice, see Fig. 2. In order to facilitate the installation of the two pieces of equipment, and in view of the fact that the ejector separator tank is the equipment room design equipment and the opening ejector is the purchased equipment, the opening ejector orifice requires the manufacturer to design a welding neck flange, and the corresponding orifice of the ejector separator tank is designed as a lap joint flange. According to the above design, the problem of misalignment of bolt holes caused by installation errors in the process of equipment connection is avoided, and the efficiency of equipment installation is improved.

2. Application of lap joint flanges on pipe fittings

Figure.3 Applications of loose flanges on pipe fittings
In the slag and gray water treatment unit, one of the special tee fittings is directly connected to the high-pressure flash tank, and the other one is directly connected to the angle valve. Figure 3 Angle valve for the standard, flange is generally butt weld flange, the special tee pipe fittings connected to the pipe design into a loose flange can solve the above problem. In addition, the special tee in order to resist black water erosion set, service for a certain period of time need to be replaced, the special tee pipe fitting set on the slip on flange, in the subsequent maintenance, maintenance process will also be very convenient.

3. Lap joint flange in the application of metal hose

In the coal pressurization and coal into the unit and gasification and syngas scrubbing unit set up flange metal hose, the conventional design of the metal hose end designed to butt-welding flange, the other end should be designed as a loose flange, here consider the metal hose for wear parts, after a certain period of time need to be replaced, through the above design will facilitate the replacement of the bolt hole alignment.

Figure.4 Loose flange in the application of metal hose

4. Selection of loose flange

Table 1 is a loose flange sealing surface form and its scope of application, as can be seen from Table 1, loose flange is generally used in low-pressure applications, including slip-on ring lap joint flange maximum allowable nominal pressure of PN16, the three examples of loose flange nominal pressure of PN20, visible flat welded ring loose flange does not meet the pressure requirements, the domestic standards for butt-welding ring loose flange maximum allowable nominal pressure up to PN100 ( Class 600), the highest allowable nominal pressure of the foreign ASME standard butt-welding ring loose flange can reach Class 2500, it can be seen that the butt-welding ring loose flange to meet the pressure requirements, therefore, the above three examples are selected to butt-welding ring loose flange.
Table.1 Loose flange sealing surface form and its scope of application

Number	Standards	Flange type	Sealing surface form	Nominal pressure	Nominal diameter
1	HG/T20614-2009	Slip-on ring loose flange	RF surface	PN6-PN16	DN10-DN600
			Male and Female Face	PN10-PN16	DN10-DN600
			Tongue and groove face
		Butt welded ring loose flange	RF surface	PN6-PN40	DN10-DN600
2	HG/T20635-2009	Butt welded ring loose flange	RF surface	Class 150 C1ass 300	DN15-DN600
3	SH/T3406-2013	Butt welded ring loose flange	RF surface	Class150 Class300 Class600	DN15-DN600
			RTJ surface
4	ASME B16.5	Butt welded ring loose flange	–	Class150-Class1500 Class2500	DN15-DN600 DN15-DN300

5. Conclusion

• (1) Loose flanges can be set on directly connected equipment, directly connected pipe fittings and metal hoses to facilitate construction and installation, while bringing convenience to subsequent pipe replacement and maintenance;
• (2) Loose flange due to its poor stress resistance, recommended for use in low and medium pressure occasions, should be avoided in the bending or torsional stress of the pipe.

In addition, stainless steel, Ti, or special metal materials on the pipeline, consider the price of these materials is relatively high, the flange material to 20 # + galvanized, only the welded ring and the pipeline with the same material, which can reduce costs. The above-mentioned loose flange application examples hope to have some reference significance to the selection of loose flange for similar occasions.
Authors: Li Qiang, Wang Wei, Chen Xie, Lao Yangyang