CN100391929C - Terephthalic acid drying method - Google Patents

Abstract

The invention discloses a drying method of terephthalic acid, which comprises the following steps: 1) entering terephthalic acid slurry around the outlet of filter machine into cylinder drier or rotary steam tubular drier; drying at partition-wall typed exchanging pattern to critical moisture content; 2) condensing; adsorbing; heating; turbining reacting waste gas as dried gas; transmitting terephthalic acid into fluid bed drier through rotary transmitter; proceeding cross flow with dried flow from steam turbine; drying. The invention improves the efficiency of heat exchanging mass in the drying course, which reduces PTA energy consumption to utilize waste heat completely.

Description

Terephthalic acid drying method

technical field

The present invention relates to a method for drying terephthalic acid.

Background technique

Aromatic carboxylic acids are important organic compounds and raw materials for the production of various chemical products, among which terephthalic acid (TA) has the largest output and is the most widely used. The world's production of terephthalic acid (TA) has reached 20 million tons per year. TA is mainly used for polymerization with ethylene glycol to produce ethylene terephthalate (PET). This polyester product is an important textile Fiber raw materials and packaging and container raw materials. TA can be produced by catalytic oxidation of p-xylene in air or other molecular oxygen sources under high temperature and high pressure conditions. Since Saffer of Mid-Century Company disclosed a method of oxidizing p-xylene to produce terephthalic acid in US Pat.

In the above-mentioned production process, the reaction is carried out in the liquid phase, and the TA produced by the reaction is finally crystallized out of the system in the form of a solid. In industry, the pure product purified terephthalic acid is obtained by filtering and drying. The drying process is generally a drum dryer or Rotary Steam Tube Dryer. Since the filtered TA contains a large amount of water (more than 10% in mass content), its latent heat of evaporation is huge, and most of the above-mentioned drying methods adopt the method of indirect heating, by setting tubes or partition walls in the dryer to provide heat with saturated steam, heat exchange The efficiency is lower, especially in the falling speed drying section, the heat loss is larger, and the heat transfer rate is lower, which increases the energy demand and heat transfer area of the process. In addition, the drier required by the current drying technology still has the problems of large volume and complicated structure.

Contents of the invention

The object of the present invention is to provide a method for drying terephthalic acid, so as to effectively improve the heat and mass transfer efficiency of the drying process and reduce the energy consumption of PTA drying.

The method for terephthalic acid drying of the present invention, its step is as follows:

1) The terephthalic acid slurry at the outlet of the filter enters the drum dryer or the rotary steam tube dryer first, and is dried to the critical moisture content by means of partition heat exchange;

2) Use the condensed, absorbed, heated and turbine reaction exhaust gas produced during the oxidation of p-xylene as the drying gas, and the terephthalic acid that has been preliminarily dried by a drum dryer or a rotary steam tube dryer is conveyed by a screw The dryer is sent to the fluidized bed dryer, and the drying gas from the steam turbine is cross-flowed for drying.

In the drying process of the present invention, there is a steam heating tube inside or on the wall of the drum dryer or the rotary steam tube dryer, and the low-pressure steam of the steam heating tube and the terephthalic acid slurry flow in reverse to exchange heat. part is evaporated, and the moisture content decreases. This heat exchange method can make the material dry to near the critical moisture content.

The main component of the exhaust gas output from the steam turbine is nitrogen, and it also contains a very small amount of carbon monoxide, carbon dioxide, and water. This gas has strong hygroscopic potential and certain energy, which is very suitable for use as a dry gas for fluidized drying.

In the fluidized bed, the wet material enters from the upper part of the fluidized bed, and the dry gas blows in from the lower part of the fluidized bed. The cross-flow operation of the two makes the material fluidized and obtains better transfer characteristics. Because the horizontal multi-chamber fluidized bed dryer has higher heat and mass transfer efficiency and higher drying speed, especially below the critical moisture content, it can greatly reduce the drying time. The fluidized bed drying in the present invention It is better to use a horizontal multi-chamber fluidized bed dryer.

The present invention provides a method for fluidized drying of PTA (purified terephthalic acid) by making full use of exhaust gas. This drying method can effectively utilize the energy of the tail gas of the reactor and improve the heat and mass transfer in the drying process. Efficiency, reduce the energy consumption of PTA drying, and realize the full utilization of waste heat.

Description of drawings

Fig. 1 is a schematic diagram of the process flow of the present invention.

Detailed ways

Fig. 1 has provided the technological process of implementing the present invention, and this process comprises three units: steam turbine 1, drum dryer 2, horizontal multi-chamber fluidized bed dryer 3. The auxiliary equipment of fluidized bed dryer includes screw feeder, blower, cyclone separator and bag filter. There is an indirect heat exchange device in the drum dryer.

The technological process of terephthalic acid drying is as follows:

1) The terephthalic acid slurry at the filter 4 outlet first enters the drum dryer 2 and dries to near the critical moisture content;

2) The terephthalic acid that has been preliminarily dried by the drum dryer is sent to the fluidized bed dryer 3 through a screw conveyor, and is dried in a cross-flow with the drying gas from the steam turbine 1 .

Example

With an annual output of 600,000 tons (annual production time 7,600 hours) of terephthalic acid, the original drying process is to use a drum dryer to directly dry to the target humidity (0.1%), and all the required heat is provided by indirect heat exchange with low-pressure steam. The energy is about 4190Kw/h, and the amount of steam required is 7.15t/h.

Adopt the method of the present invention to dry terephthalic acid, relevant process parameters are listed as follows according to unit sequence:

1. Drum dryer

Its operating parameters and output are shown in Table 1

Table 1 Operating parameters and output of drum dryer

2. Horizontal multi-chamber fluidized bed dryer

The equipment parameters and operating conditions are shown in Table 2, and the output parameters are shown in Table 3

Table 2 Parameters and operating conditions of horizontal multi-chamber fluidized bed dryer

Table 3 Output index of horizontal multi-chamber fluidized bed dryer

The above test shows that the method of the present invention saves about 1518kw/h of energy compared with the original process. It can reduce the low-pressure water vapor of public works by 2.56t/h.

Claims (2)

1. the method for terephthalic acid drying, its step is as follows: 1) The terephthalic acid slurry at the outlet of the filter enters the drum dryer or the rotary steam tube dryer first, and is dried to the critical moisture content by means of partition heat exchange; 2) Use the condensed, absorbed, heated and turbine reaction exhaust gas produced during the oxidation of p-xylene as the drying gas, and the terephthalic acid that has been preliminarily dried by a drum dryer or a rotary steam tube dryer is conveyed by a screw The dryer is sent to the fluidized bed dryer, and the drying gas from the steam turbine is cross-flowed for drying. 2. The method for drying terephthalic acid according to claim 1, characterized in that said fluidized bed dryer is a horizontal multi-chamber fluidized bed dryer.

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