Automatic variable load control of the hottest oxy

2022-08-10
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Automatic variable load control of oxygen production

summary

oxygen production is closely related to converter smelting, and the characteristics of oxygen consumption in converter smelting are large consumption and large change range, which is closely related to the rhythm of converter smelting production. It is an intermittent oxygen load, so there are often two phenomena in oxygen production: the length of the straight section of LC sample, oxygen emission or short supply. The former is not conducive to the energy saving and consumption reduction of oxygen production and economic operation indicators, while the latter affects the converter smelting production, and even affects the production organization and economic benefits of the whole converter steelmaking production line. In the reconstruction and expansion with foreign capital, Laigang introduced the 12000m3/h air separation unit of Linde company in Germany in 1994 to meet the oxygen supply of Laigang with an annual output of 2million tons of steel. During the technical exchange and business negotiation, Linde company will provide a complete set of air separation equipment, Laigang will be responsible for the plant design and construction, and German experts will be responsible for the project supervision and system commissioning. In order to solve the contradiction between oxygen production and oxygen consumption in converter steelmaking, while increasing the volume of liquid oxygen storage tank, it is proposed to add an automatic variable load system for oxygen production in the control system of the air separation unit to the German side. The system adopts the distributed control system (DCS) of Bailey company to realize the automatic control of the whole process of oxygen production. The automatic variable load system for oxygen production is to automatically adjust the production and operation workers to nearly support half of the carton industry according to the change of oxygen consumption of users. In fact, the operation parameters are approaching the best point in the process of automatic control to realize optimal operation

1 automatic variable load control principle

when designing the automatic variable load control program software, the software is divided into several modules according to different tasks, and its structure is shown in Figure 1. In the figure, the automatic load change control program is divided into display service modules; Operation point calculation module; Process model; Transmission controller module and optimization controller

1.1 the display service module

provides the operator with an operation interface to display the process flow chart, process parameter values and change trends, and process alarm parameters. Various gas pipelines are displayed in different colors, and the required local screen display is selected in the process flow screen according to the operation needs

1.2 operation point calculation module

it has a set of input parameter calculation model, which reviews the target output of the main products input by the operator based on experience, such as liquid nitrogen (LN), liquid oxygen (LO), high pressure oxygen (HPA) and gas oxygen (go), and calculates the allowable minimum, maximum and target output values of each output, so as to prevent the value input by the operator from seriously inconsistent with the process requirements. The calculation results are related to the design capacity, the current process state and the last calculation model values. When the input parameter values are seriously inconsistent with the process values, the display screen will prompt an error message. There are four input parameter calculation models, The expression of liquid oxygen model is as follows

flo=[(F1-F2)/k1-f3-k2

, where Flo is the liquid oxygen output; F1 is the air flow at the outlet of molecular sieve; F2 is the subcooled air volume of expander; F3 is the oxygen flow at the inlet of oxygen compressor; K1 and K2 are coefficients.

the calculation result of this model provides the operator with a liquid oxygen output value consistent with the design capacity and current process.

the calculation model expression of liquid nitrogen input parameters is

FLN=[ (F1 - F2)/k3 - k4

where FLN is the output of liquid nitrogen; K3 and K4 are coefficients

the theoretical output value of liquid nitrogen is the ratio of the difference and coefficient between the outlet air volume of molecular sieve and the subcooled air volume of expander; Minus the loss coefficient, it is the actual output of liquid nitrogen

the calculation model of hyperbaric oxygen input parameters is

fhpa=[(F1-F2)/K5 - F4 - k6

where FHPA is the output of hyperbaric oxygen; F4 is the liquid oxygen flow at the inlet of the liquid oxygen pump; K5 and K6 are coefficients

since the oxygen products in the production process of the air separation unit are liquid oxygen, gas oxygen and high-pressure oxygen, the output of the three products in the input parameter calculation model is interrelated, but they all take the air volume at the outlet of the molecular sieve and the subcooled air volume of the expander as the basic calculation parameters

the calculation model of gas oxygen input parameters is

fgo= - f3-f4-k8

where FGO is the gas oxygen output; F is the air flow at the outlet of the air compressor; K7 and K8 are coefficients

4 input parameter calculation model is to calculate the output value of each product in the current production process according to the design capacity and operating conditions of the air separation unit, so that the operator can timely understand the operating conditions and product output. There are three design conditions for this air separation unit, as shown in Table 1:

condition a in the table is the best design condition (one turbine is working and the other is standby), condition B is the operation condition that the output is reduced to 70% as required, and condition C is the design condition when 800m3/h liquid oxygen is required to be produced (two turbines are working at the same time). Since the produced gas oxygen pressure is 145kpa, the gas oxygen needs to be converted into high-pressure oxygen in the process of oxygen transmission

1.3 process model module

process model module is composed of a series of model function blocks, which can be divided into state model and calculation model. The automatic variable load control program controls the change of process load by controlling the output, quality and speed of several main products, and the control of several main links in the process flow is inaccurate. There are 7 state models and 7 calculation models in total. They calculate the expected state values of these control links in the process according to the state model according to the output target required for the working condition, the principle of material balance and refrigeration capacity balance, and the relevant parameters of the main process links

1.3.1 state model

the seven state models in the process model are: air purification state model, crude argon state model, liquid argon state model, refrigeration balance state model, turbine air state model, turbine bypass air state model and process gas state model. These seven models play a decisive role in ensuring the stability of the process. The seven state models are represented by S1,..., S7 respectively. The air purification quantity S1 is a function of the output of gas oxygen and liquid oxygen, and its expression is

s1=f (K1, FGO, Flo, C1)

where K1 is the coefficient; C1 is the amount of air purification under working conditions

crude argon state model S2 is only related to air purification S1

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