Preface
To satisfy the new type aircraft's demand for oxygen and nitrogen, oxygen and nitrogen making car for military use can generate oxygen and nitrogen with air as raw material and using the method of deep freezing liquefied and cryogenic distillation separation.
Based on the STAR - 90 simulation supporting system, we developed a simulator for military-used oxygen and nitrogen making car after making some simplification of the car's actual system. This simulator can simulate the process of generating oxygen and nitrogen; faithfully reflect the dynamic response to object's fault phenomenon and the reaction to it. Production personnel can be trained for start-up, normal operation and fault handling in the simulator in order to fully grasp the running characteristics of the simulation object as soon as possible.
1. General Introduction
The oxygen and nitrogen making car is mainly composed of air precooling system, molecular sieve purification system, air distillation system, cooling system and so on.
Its technological process is as follows: this car uses the screw compressor as gas supply; the molecular sieve adsorbs moisture and carbon dioxide; the reflux gas comes into the expander for refrigeration and compressed inside the cryogenic liquid pump; the single distillation column with auxiliary nitrogen condenser form the distillation of gas oxygen, nitrogen and liquid oxygen, liquid nitrogen gas.
2.The Composition of the Training Simulator
This training simulator includes hardware system and software system.
Hardware system includes main computer, virtual control operating station, simulation control panel, STAR - 90 interface system; Software system includes simulation supporting software, mathematical model software, virtual control interface software, etc.
The following will focus on the mathematical model software.
3.Introduction of the Mathematical Model
3.1 Brief Introduction of STAR – 90 Modeling And Simulation Supporting Platform
The development of mathematical model for training simulator is built on the basis of the STAR - 90 modular modeling and simulation supporting platform. The method of STAR - 90 modular modeling is derived from the idea of the decomposed system.
According to the thought of system decomposition, the system is decomposed into several modules connected by the supporting system, each of which can function independently and be debugged separately. This method can reduces the difficulty of modeling, facilitate model check, debugging and modification, and the algorithms for various modules can be repeatedly used, improving the efficiency of the software development.
3.2 Introduction of the Simulation Model
According to the making process and the simulation range, this model can be divided into four parts: air precooling unit, the molecular sieve purification system, distillation unit system and turbine expander system.
3.2.1 Air Precooling Unit
Air precooling unit is an air compression and water purification equipment based on the corresponding relationship between the saturated vapor pressure and the water temperature. This unit forces to cool down and compress air; then makes the vapors in the compressed air saturated and condensed; finally separates water.
3.2.2 Molecular Sieve Purification System
The role of molecular sieve purification device is to remove a small amount of gas impurities in the air such as water, acetylene and carbon dioxide, in order to ensure the normal conduction of air separation. The working principle is: when the compressed air goes through the fixed adsorption bed of the adsorber, the small amount of impurities such as H2O, C2H2, CO2 will be absorbed into the adsorbent hole by making use of the adsorbent porous surface's characteristics of choosing the components for adsorption. In this way, the goal of cleaning the air can be achieved.
3.2.3 Distillation Unit System
The distillation unit system is the most important part in the simulator system and also the most complex algorithm in the mathematical model. Fractionating column is the equipment using the method of extending the contact time and increasing the contact space to strengthen the heat and mass transfer between gas and liquid in order to realize the separation of oxygen and nitrogen in the air.
3.2.4 Turbine Expander
Turbine expander is a machine gaining low temperature by outputing external work and producing cold quantity through the compressed gas (medium)'s adiabatic expansion inside the machine. Its working principle is, the working medium gains kinetic energy through its flow in turbine expander, and outputs external work by working shaft.
3. Summary
The training simulator for oxygen and nitrogen making car is made according to the working medium's process and by using special and general algorithms, with the following basis: STAR - 90 simulation supporting system, the real oxygen and nitrogen making car's working mechanism, the principle of mass conservation, energy conservation, and phase equilibrium. The simulator has good static precision and dynamic characteristic. It can make relatively real simulation of the nitrogen and nitrogen making car's normal operation and all kinds of failure phenomenon such as start up, stop and operation adjustment.
