Method and device for generating compressed nitrogen by the cryogenic decomposition of air
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Solution Overview
Problem
Current methods for obtaining pressurized nitrogen through low-temperature air separation are inefficient in terms of energy consumption and can lead to operational difficulties due to the use of bath evaporators, which are not optimal for energy use and allow high-boiling substances like propane to accumulate, affecting system safety and product yield.
Innovation Solution
The implementation of a forced-flow evaporator as a low-pressure column top condenser, combined with a barrier floor section in the high-pressure column to retain high-boiling substances, and the use of a subcooling countercurrent indirect heat exchange to prevent pre-liquefaction of air, ensuring the air enters the high-pressure column in a gaseous state, thereby reducing energy consumption and maintaining system safety.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bath evaporator is used as a low-pressure column top condenser, then the system is operationally reliable, but energy consumption increases due to hydrostatic head in the liquid bath
Solution Approach 1:
The invention extracts the liquid bath from the evaporation process and replaces it with a forced-flow evaporator design. This removes the source of hydrostatic head pressure while maintaining the condensation function, thereby eliminating the energy penalty associated with bath evaporators.
Solution Approach 2:
The invention replaces the passive bath evaporator mechanism with an active forced-flow evaporator system. This substitution allows for controlled liquid flow without relying on hydrostatic pressure, reducing energy consumption while maintaining operational reliability.
2Ease of operation
If a bath evaporator is used as a low-pressure column top condenser, then the system is simple to operate, but high-boiling substances like propane accumulate and affect system safety
Solution Approach 1:
The invention extracts the liquid bath that causes high-boiling substance accumulation and replaces it with a forced-flow evaporator. This design change prevents propane and other heavy components from accumulating in the condenser, thereby improving system safety while maintaining ease of operation.
Solution Approach 2:
The invention changes the operational parameters of the evaporator from passive bath-based operation to active forced-flow operation. This parameter change alters the flow dynamics and temperature distribution, preventing the accumulation of high-boiling substances and improving system safety.
3Productivity
If air is pre-liquefied before entering the high-pressure column, then the separation process is enhanced, but energy consumption increases and operational safety decreases
Solution Approach 1:
The invention applies preliminary action by pre-heating the air stream using waste heat from the nitrogen product before it enters the high-pressure column. This pre-heating prevents excessive cooling and pre-liquefaction, maintaining separation efficiency while reducing energy consumption and improving safety.
Solution Approach 2:
The invention implements feedback control by monitoring the temperature and composition of the air stream entering the high-pressure column. This feedback mechanism allows for adjustment of the pre-heating process to prevent pre-liquefaction, optimizing separation efficiency while minimizing energy consumption and safety risks.
4Use of energy by moving object
If a forced-flow evaporator is used as a low-pressure column top condenser, then energy consumption is reduced, but the system complexity increases
Solution Approach 1:
The invention replaces the simple but energy-inefficient bath evaporator with a forced-flow evaporator system. While this increases device complexity, the energy savings justify the added complexity, and the forced-flow design actually simplifies certain operational aspects by eliminating the need for large liquid baths.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces energy consumption by approximately 3.2% at 10 bar and 2.2% overall, while effectively removing high-boiling substances and preventing pre-liquefaction, ensuring a stable and efficient process for obtaining compressed nitrogen with minimal liquid production.
Implementation Method 1
The use of a forced-flow evaporator as a low-pressure column overhead condenser allows for a particularly low pressure differential between the evaporating and condensing streams
Implementation Method 2
the gaseous nitrogen stream from the high-pressure column is preheated in a subcooling counterflow system in an indirect heat exchange with the oxygen-enriched liquid stream
Implementation Method 3
a barrier plate section is provided that retains the high-boiling substances, especially propane, in the sump of the high-pressure column
Data Source
Figure 1a
Figure 1b
Figure 2
AI summary
The method and apparatus are used for the production of pressurized nitrogen by low-temperature decomposition of air in a distillation column system. The distillation column system comprises a high-pressure column (4), a low-pressure column (6), a main condenser (5), and a low-pressure column top condenser (7), both of which are designed as condenser-evaporators. Compressed and purified feed air (1) is cooled in a main heat exchanger (2) and introduced, at least predominantly, in gaseous form into the high-pressure column (4) (3). An oxygen-enriched liquid stream (11, 13) is drawn from the high-pressure column (4) and introduced into the low-pressure column. A gaseous nitrogen stream (17, 26A, 26B, 27) is drawn from the high-pressure column (4), heated in the main heat exchanger (2), and withdrawn as the gaseous pressurized nitrogen product (28, 31). The evaporation chamber of the low-pressure column head condenser (7) is designed as a forced-flow evaporator.The high-pressure column (4) has a barrier plate section (8) located directly above the point where the feed air (3) is introduced, and comprising one to five theoretical or practical plates. The oxygen-enriched liquid stream (11), which is introduced into the low-pressure column (6), is drawn from the high-pressure column (4) above the barrier plate section (8). A purge stream (9A) is drawn from below the barrier plate section (8) and removed from the distillation column system (9B). The gaseous nitrogen stream (26A, 26B) is preheated in a subcooling counterflow unit (12) by indirect heat exchange with the oxygen-enriched liquid stream (11) from the high-pressure column (4) before being heated in the main heat exchanger (2).