Pulping Liquor Concentration via MVR and Multi-Effect Evaporation
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Solution Overview
Problem
The wood pulping process generates a wastewater stream with low solids concentration that needs to be efficiently concentrated for disposal, as conventional methods struggle to effectively concentrate pulping effluent beyond 1.5% dry solids content.
Innovation Solution
A system utilizing mechanical vapor recompression (MVR) evaporators for initial concentration to 15-20% dry solids, followed by a multi-effect train of forced circulation solids concentrators, linked by a gas stripper that utilizes contaminated vapor streams to enhance thermal energy and further concentrate the liquor to 60-70% dry solids, allowing for efficient incineration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional evaporation methods are used to concentrate pulping effluent, then some concentration is achieved, but the process cannot effectively concentrate liquor beyond 1.5% dry solids content
Solution Approach 1:
The concentration process is divided into two distinct stages: a pre-concentration stage using MVR evaporators to reach 15-20% solids, and a final concentration stage using forced circulation solids concentrators to reach 60-70% solids. This segmentation allows each stage to be optimized for its specific concentration range, overcoming the limitation of conventional single-stage methods.
Solution Approach 2:
The process utilizes parameter changes by transitioning from MVR technology (effective at low concentrations) to forced circulation evaporators (effective at high concentrations). The system adapts the evaporation mechanism and operational parameters according to the concentration level, enabling effective concentration across the entire range from 1.5% to 60-70% solids.
2Use of energy by moving object
If multi-effect trains are used to concentrate liquor, then thermal efficiency is improved, but steam economy is limited by the number of thermal effects
Solution Approach 1:
The contaminated vapor stream from the gas stripper, which was previously a waste product, is converted into a useful thermal energy source. This vapor is directed to the first effect of the multi-effect train to heat the concentrated liquor, effectively adding a fourth thermal effect and improving steam economy without requiring additional energy input.
Solution Approach 2:
The gas stripper serves dual functions: it removes contaminants from the liquor (original function) and generates a contaminated vapor stream that provides thermal energy for the concentration process (additional function). This multi-functionality maximizes the utility of the gas stripper and improves overall process efficiency.
3Productivity
If high concentration is achieved for incineration, then disposal efficiency is improved, but high temperature-induced scaling and suspended solids concentration occur
Solution Approach 1:
The gas stripper performs preliminary removal of contaminants and suspended solids from the liquor before the final concentration stage. By removing these harmful components early in the process, the subsequent high-concentration evaporation and incineration stages operate with cleaner feed, minimizing scaling and suspended solids problems.
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 process significantly increases the thermal efficiency of the concentration process, enhancing steam economy and enabling the pulping effluent to be economically and practically disposed of through incineration, while minimizing high temperature-induced scaling and suspended solids concentration.
Implementation Method 1
the pre-concentration unit comprises one or more mechanical vapor recompression (MVR) evaporators. These evaporators concentrate the liquor to where, in one example, the solids content is approximately 15-20%
Implementation Method 2
The concentrated liquor is heated and further concentrated in the multi-effect train, in one embodiment, to where the solids content is approximately 60-70%
Implementation Method 3
Steam is injected into the gas stripper and strips gases such as methanol and other volatile organics from the contaminated condensate
Implementation Method 4
the thermal energy associated therewith is utilized to heat the concentrated liquor flowing through the thermal effects and particularly a series of forced circulation solids concentrators
Data Source
AI summary
Wood pulping process including pulping wood to produce a pulping effluent or liquor. Pre-concentrating the liquor in a pre-concentration unit produces concentrated liquor, a contaminated condensate and a non-contaminated condensate. Directing the concentrated liquor to a multi-effect train of forced circulation solids concentrators that further concentrating the concentrated liquor to form a highly concentrated liquor. Directing the contaminated condensate produced by the pre-concentration unit to a steam stripper and stripping gases therefrom and in the process producing a contaminated vapor stream. Utilizing the contaminated vapor stream and its thermal energy to power the forced circulation solids concentrators of the multi-effect train.