Vapor Recompression Startup Using Pressure Reduction and Restricted Flow
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Solution Overview
Problem
The start-up of mechanical vapor recompression systems requires high electrical power due to the need for the compressor motor to match the total mass of vapor flow, leading to high operating costs and power quality issues, and current methods like VFDs are inefficient and costly.
Innovation Solution
A method involving reducing vapor density through pressure reduction and introducing a restricted vapor mass flow rate to gradually start up vapor-recompression units, using means such as vacuum pumps or condensers to minimize power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional VFDs are used to control compressor motor speed during start-up, then the mass vapor flow can be controlled, but the electrical power consumption remains high and power quality issues occur
Solution Approach 1:
The patent applies preliminary action by introducing a restricted vapor mass flow rate before fully operating the compressor motor. This allows the motor to start up under reduced load conditions, avoiding the high electrical power demand and power quality issues that occur during conventional full-power start-up. The restricted flow is maintained during the critical start-up phase, then gradually increased to full operational flow.
2Productivity
If the compressor motor operates at full capacity during start-up, then it can handle the total mass of vapor flow, but the electrical power consumption and operating costs increase significantly
Solution Approach 1:
The patent applies partial action by operating the compressor motor at reduced capacity during the start-up phase. Instead of immediately handling the total mass of vapor flow, the motor processes only a restricted portion of the vapor flow initially. This partial operation significantly reduces electrical power consumption during start-up, and the flow rate is then gradually increased to full capacity as the system stabilizes.
3Ease of operation
If VFDs are used to control compressor speed, then start-up synchronization is achieved, but the equipment cost and system complexity increase
Solution Approach 1:
The patent introduces an intermediary mechanism - a restricted vapor flow control system - that mediates between the vapor source and the compressor motor during start-up. This intermediary restriction allows the motor to start under controlled, reduced load conditions without requiring complex VFD electronics. The restriction can be implemented through simple flow control devices, reducing system complexity while maintaining ease of operation.
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 allows vapor-recompression units to be started up efficiently with reduced electrical power consumption and improves system reliability and efficiency.
Implementation Method 1
reducing pressure within the vapor recompression sub-system by operating the means of reducing vapor density through pressure reduction
Implementation Method 2
The means of reducing vapor density through pressure reduction may utilize a condenser
Data Source
AI summary
A method for starting up vapor-recompression units comprises: providing a vapor recompression sub-system comprising one or more vapor-recompression units, wherein the vapor recompression sub-system has a vapor inlet and a compressed-vapor outlet; providing a means of reducing vapor density through pressure reduction in vapor communication with the vapor recompression sub-system; reducing pressure within the vapor recompression sub-system to reach a sub-system pressure selected from 0.1 kPa to 1000 kPa; introducing a vapor mass flow to the vapor recompression sub-system at a restricted vapor mass flow rate; starting up the vapor recompression sub-system while maintaining the restricted vapor mass flow rate for a start-up time period; and then, following the start-up time period, introducing additional vapor mass flow to the vapor recompression sub-system to reach a full vapor mass flow rate. The restricted vapor mass flow rate is from 0.1% to 90% of the full vapor mass flow rate.