AU2018100802A4

AU2018100802A4 - A method and system for the concentration of juice

Info

Publication number: AU2018100802A4
Application number: AU2018100802A
Authority: AU
Inventors: Ambrosios Kambouris
Original assignee: Botanical Water Technologies IP Ltd
Current assignee: Botanical Water Technologies IP Ltd
Priority date: 2018-06-15
Filing date: 2018-06-15
Publication date: 2018-07-19
Anticipated expiration: 2026-06-15
Also published as: AU2018100802B4

Abstract

A method and system for concentrating a liquid, especially sugar cane or sugar beet juice or distillery spent wash, the method including the steps of subjecting the juice to forward osmosis to remove a first percentage of water and then using at least one evaporator system to remove a second percentage of water. "iC hT|, - EWnMu i m T Figure 3 Life Cycle Cost per m3 of clean water reused ($) $30 - $28 $21 $20 $10 $3.3 $0 -1 -j Figure 4

Description

FIELD OF THE INVENTION [0001] The present invention relates to a process and apparatus for concentrating liquid solutions containing dissolved solids to very low water content.

BACKGROUND TO THE INVENTION [0002] The process of concentrating liquid solutions containing dissolved solids to very low water content, traditionally involves the use of evaporators. Due to rising costs in electricity, gas and water, this method of concentrating is becoming cost prohibitive for the concentrating industry, despite achieving final water concentration levels of between 10 and 30 percent in the processed liquid solution.

[0003] The most common evaporators being used to concentrate juice or spent wash (ferments with alcohol removed) are the multi-effect evaporators where water is boiled in a sequence of vessels, each held at a lower pressure than the last. Such evaporators, despite being more energy efficient than single evaporators, are still large consumers of energy (power, steam, water, etc.) and are limited in efficiency to a maximum number of seven effects in series. This limitation to the number of effects is due to the cost-benefit analysis of adding additional effects in commercial practice.

[0004] It is proposed that further efficiencies in evaporator use can be achieved by options other than increasing the number of effects on any evaporator.

[0005] The object of this invention is to alleviate the above problem, or at least provide the public with a useful alternative by including a pre-evaporator concentration step.

SUMMARY OF THE INVENTION [0006] In a first aspect the invention comprises a method for concentrating juice or spent wash the method including the steps of:

(a) providing a juice for concentration;

(c) subjecting the juice to a forward osmosis step to remove water from the juice and provide concentrated juice;

(d) subjecting the concentrated juice to an evaporation process to remove yet more water.

[0007] In preference the evaporation process includes single or multiple evaporators in series.

2018100802 15 Jun 2018 [0008] In a further aspect of the invention there is proposed a system for producing concentrated juice the system comprising:

a forward osmosis apparatus to remove a percentage of water from the juice to produce concentrated juice;

at least one evaporation apparatus adapted to receive the concentrated juice and remove yet more water from the concentrated juice.

[0009] In preference the juice is sugar cane juice or sugar beet juice or distillery spent wash.

It should be noted that any one of the aspects mentioned above may include any of the features of any of the other aspects mentioned above and may include any of the features of any of the embodiments described below as appropriate.

BRIEF DESCRIPTION OF THE DRAWINGS [0010] Preferred features, embodiments and variations of the invention may be discerned from the following Detailed Description which provides sufficient information for those skilled in the art to perform the invention. The Detailed Description is not to be regarded as limiting the scope of the preceding Summary of the Invention in any way. The Detailed Description will make reference to a number of drawings as follows.

[0011] Figure 1 is a diagram of the forward osmosis and recovery of the draw solution according to the present invention;

[0012] Figure 2 is a diagram illustrating alcohol production by fermentations;

[0013] Figure 3 is a flow diagram of spent still bottoms processing post removal of alcohol by distillation; and [0014] Figure 4 illustrates the cost comparison of using evaporator or FO techniques.

DETAILED DESCRIPTION OF THE INVENTION [0015] The following detailed description of the invention refers to the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings and the following description to refer to the same and like parts. Dimensions of certain parts shown in the drawings may have been modified and/or exaggerated for the purposes of clarity or illustration.

[0016] The present invention is for a process and apparatus for the concentration of

2018100802 15 Jun 2018 juices in particular sugar juice or sugar beet juice or spent wash (ferments with alcohol removed) using Forward osmosis as a pre-evaporator concentration step. The Forward osmosis (FO) step is an osmotic process that, like reverse osmosis, uses a semi-permeable membrane to effect separation of water from dissolved solutes. The driving force for FO separation is an osmotic pressure gradient created using a draw solution of high concentration. This osmotic gradient is used to induce a net flow of water through the membrane into the draw solution, thus effectively separating the feed water from its solutes.

[0017] The FO technology has not been used in series with an evaporator especially in the sugar and sugar-beet and spent wash concentration industry.

[0018] The FO concentration step proposed may concentrate juices from their physiologically acquired Brix at maturity to a final 40 or 50 Brix. This FO concentration process alone, is not useful for sugar juice or beet juice processing, that aims to produce raw crystalline sugar or molasses and requires much less water in the concentrate for further processing to make the crystallisation process economically achievable. Multi-effect evaporators however on their own, can concentrate such juices to desirable higher Brix levels i.e. 70 to 85 Brix.

[0019] The advantage of FO concentration includes the lower cost of the equipment and the running costs during operation. These costs have been compared in the literature as being in the order of 9 times cheaper than an evaporator (Figure 4). It is thus environmentally sustainable and economical to include a pre-concentration step that will achieve an initial concentration of the juices or spent wash at a low operating cost prior to the use of an evaporator or a multi-effect evaporator that will then augment the concentration process to achieve the desired 70 to 85 Brix.

[0020] There are several advantages in using FO technology prior to evaporator use in series with an evaporator. These include:

(a) The evaporator has less volume to evaporate and could be sized down.

(b) The number of effects can be reduced as less surface area is required.

(c) The flow rate through existing evaporators can be increased due to lower water removal requirements.

2018100802 15 Jun 2018 (d) Reduced energy, steam, gas water requirements during processing fixed volume liquids.

[0021] The evaporator is a piece of equipment that is used to convert a liquid substance such as water into its gaseous-form. The liquid water is evaporated, or vaporised, into a gas form in that process. The vaporised water is then condensed and collected as a liquid again.

[0022] Briefly, the evaporators are fed a solution requiring concentrating across a heat source, converting the water in the feed into vapour. The vapour is removed from the rest of the solution and is condensed while the now-concentrated solution is either fed into a second evaporator or is removed.

[0023] An evaporator may consist of four sections. These are: firstly, the heating medium, which is often steam that passes through parallel conducting tubes or plates or coils. Secondly, a concentrating and separating section which removes the vapour being produced from the feed solution. Thirdly, a condenser that condenses the separated vapour. Finally, a vacuum system or pump to increase circulation and reducing the pressure within the evaporator and reducing the boiling point of the water.

[0024] There are many different types of evaporators in use. These include:

natural/forced circulation evaporators, falling film evaporators, rising film (long tube vertical) evaporators, climbing and falling film plate evaporators, multi-effect evaporators and agitated thin film evaporators and others not mentioned.

[0025] The most commonly used evaporator type used in sugar cane juice concentration, sugar beet juice concentration and alcohol distillation spent wash concentration, are the multi-effect evaporators.

[0026] These multi-effect evaporators unlike single-stage evaporators, can be made of up to seven evaporator stages or effects. The reason for using multiple effects during evaporation is because energy consumption for single-effect evaporators is very high and is most of the cost for an evaporation system.

[0027] Multiple effects combined saves heat and energy. In fact, a dual effect evaporator can reduce energy consumption of one single evaporator by 50%. Adding to this another effect can reduce energy consumption to 33% and so on until seven effects are in parallel and no further savings can be obtained due to the actual cost of each effect. The energy saving can be calculated.

2018100802 15 Jun 2018 [0028] Feeding liquid into the multiple-effect evaporators can be either by the forward or backward feeding approach.

[0029] The forward feeding approach means that feed liquid enters the system through the first effect, which is at the highest temperature. This feed liquid is then partially concentrated as some water is removed before being fed into the lower temperature second effect and so on. The second effect is heated by the vapour removed from the first effect (hence the saving in energy expenditure). This continues throughout the effects in series and the combination of lower temperatures and higher viscosities in subsequent effects provides an increase in the heating surface area.

[0030] In contrast, in backward feeding, the last effect has the lowest temperature and is fed the liquid being concentrated and the liquid moves effects whilst the temperature in these effects increases. The final concentrate is collected in the hottest effect, which provides an advantage in that the product is highly viscous in the last stages, and so the heat transfer is better.

[0031] The schematic process in Figure 1 shows the feed liquid (still bottoms) passing through the FO unit. A FO membrane allows interfacing between the feed solution and the draw solution.

[0032] The draw solution passing through the FO needs to be regenerated and this can occur through the removal of pure water and leaving the salts behind. Water removal from the draw solution can be achieved by reverse osmosis, nano-filtration, membrane distillation, or by any other means that allows this to happen.

[0033] Advantages in using FO rather than RO is the fact that FO membranes do not foul as readily as RO membranes when in direct contact with spent wash or juice which contain very high levels of organic material and suspended solids. This is because particles are likely to be pushed into the pores of RO membranes due to the high pressure exerted on the liquid during filtration.

[0034] In contrast, FO membranes are resistant to fouling because there is much less physical pressure on the liquid during FO filtration and suspended solids seldom enter pores of the membrane. Reversed flushing with clean water daily, often clean the pores of the membrane more successfully than with RO. Thus, using FO will result in consistent water flux from the spent wash or juice, resulting in drier solution entering the evaporator. Drier

2018100802 15 Jun 2018 solutions will require less energy to completely dehydrate.

[0035] FO membranes are functional within the temperature range of 1 to 95 Celsius and are highly resistant to high chemical concentrations and extreme ph. Spent wash temperatures often aim to reach around 80 Celsius during ethanol distillation due to the lower boiling point of ethanol relative to water.

[0036] Heat energy from the spent wash can be harvested and added to the draw solution post FO filtration and prior to draw solution regeneration when using membrane distillation. The energy in reducing the temperature from around 80 Celsius to 25 Celsius, can be harvested using heat exchangers such as tube in tube type or other types. This eliminates the requirements for expensive heat resistant RO or NF membranes if these are required. The heat harvested can then be used where required to offset the cost of running the FO and RO system. Alternatively, heat harvested from the evaporator condensates can be used to heat the draw solution prior if membrane distillation is the preferred draw solution regenerative process.

[0037] Membrane distillation is a thermally driven separation program in which separation is enabled due to phase change. A hydrophobic membrane displays a barrier for the liquid phase, allowing the vapour phase to pass through the membrane's pores. The driving force of the process is given by a partial vapour pressure difference commonly triggered by a temperature difference.

[0038] Unlike RO that requires the spent wash to be decanted, ultra-filtered or Nanofiltered as a pre-treatment to prevent membrane fouling, the FO membrane only requires either a course screen or a sand filter to function under these highly fouling conditions.

[0039] The invention can be described as a new option other than adding effects to an existing single evaporator or, a multi-effect evaporator that already has the maximum number of effects or efficiency and is energy use expensive.

[0040] Adding FO in series prior to existing evaporators to pre-concentrate, reduces the overall processing costs and capital costs of expanding evaporators. This leads to a reduction in the use of power, steam, water and heating for concentrating a given volume of juice or liquid solution.

[0041] The invention requires the use of Forward Osmosis filtration technology to preconcentrate or de-water the juice to a mid-level of concentration, prior to concentrating the

2018100802 15 Jun 2018 juice to the final desired level using an evaporator.

[0042] Sugar cane juice commercially extracted from sugar cane at maturity after the addition of chemicals and clarified is around 13 Brix. Within the evaporator, the juice is recirculated until the final Brix departing the evaporator increases to between 70 to 75 Brix.

[0043] A sugar juice concentration process was carried out. The amount of sugar cane juice processed by evaporation was 325 tonnes per hour through a multi-effect evaporator. The juice contained 87% water and for every 5.18 tonnes of water removed from the juice through the evaporator, 1 tonne of steam was consumed.

[0044] Using FO to reduce the water contents of the sugar juice by only 26% in a sugar mill that crushes 7,000 tones sugarcane per day, saved the use of 400 tonnes per day steam by a 5-effect evaporator and about 175 tonnes/day bagasse.

[0045] Plant materials are utilized on an industrial scale to produce a wide range of products including alcohol. A plant-derived material containing sugar is incubated with yeast, with the yeast metabolically converting the sugar to alcohol. A common use of fermentation is by distilleries that utilize plant sugars such as molasses to produce alcohol. First, molasses is diluted by adding water to adjust the total dissolved solids to about 7-8% before adding yeast, nitrogen and other required nutrients for fermentation to commence. At the end of this ferment, when glucose is converted to ethyl alcohol and carbon dioxide, the solution is referred to as a beer solution. The CO₂ is collected during its production and the alcohol is harvested through a distillation column. The diagrammatic representation of the process can be seen in Figure 2.

[0046] The still bottoms or spent wash from this fermentation process is a complex organic effluent that is characterised as dark brown in colour, acidic and with a high BOD and COD value. The solution is rich in organic carbon, K, Ca, Mg and S and contains N, P, Mn, Fe, Zn, Cu and traces of sugar. It also contains plant growth promoters such as indole acetic acid and gibberellic acid. The solution is not toxic, biodegradable and can be used for the following applications:

(a) Composting either by traditional means or through bio-methanation.

(b) Potash recovery through incineration of the distillery spent wash after neutralisation with lime.

(c) Fertilising soils for crops such as rice, wheat, sugarcane, ground nut, C3 and

2018100802 15 Jun 2018

C4 plants and others. The limitation is the high BOD and COD that can be overcome by diluting with irrigation water during application. The fertiliser can be wet or dry.

(d) Biogas production.

[0047] Most of the 4000 alcohol distilleries in the world use starch and sugar feedstock up to 20% concentration in water for ethanol yeast fermentation that is heated to boiling in a still to evaporate the volatile fermentation products, mostly azeotropic ethanol, that condense in a column separator and the residuals are discharged as hot still bottoms that can contain from 2-10% inorganic and organic dissolved and suspended solids composed mostly of spent yeast cells and cell parts, metabolites, fermentation by-products, and nonfermentable starch and sugar feedstock residues. Nitrogen is often added to culture yeast before fermentation and typical yeast is composed of nearly 90% protein and carbohydrates.

[0048] Following distillation to remove alcohol, this still bottom fraction is often discharged directly to a water course, decanted into heavier and lighter fractions, or is evaporated to recover the solids as animal feed, filtered to recover other fermentation byproducts from a concentrate, or biologically treated by anaerobic digestion to recover methane fuels (illustrated in Figure 3).

[0049] Concentrating still bottoms by evaporation is the standard method used in many distilleries across the world to recover water and by-products (Figure 1). Briefly, multi-effect or other types of industrial evaporators, require the still bottoms to be pre-treated by decanting or centrifugation to remove most of the solids. The concentrate produced by evaporation is composed of between 30 and 35% total solids.

[0050] Solids removed by decanting may be used as feed stock for animals. The concentrated still bottoms are often further dried using industrial dryers or traditional drying methods to produce soil or agricultural fertilisers (Figure 1).

[0051] The problem of using evaporators in the process of reclaiming water from still bottoms is the requirement of pre-treatment with a decanter or centrifuge to remove most of the solids and high-power costs and equipment maintenance (Figure 3). In a typical scenario, a multi-effect evaporator consumes 90 KWh to process 12,000 L and to concentrate to 3000 L in final volume.

[0052] As seen in Figure 4, the FO costs can vary with different types of FO membranes

2018100802 15 Jun 2018 used, however the technology is a lot cheaper than evaporation costs, when a specific membrane and conditions are optimised.

[0053] As with sugar juice and sugar-beet juice concentration, the aim of concentrating spent wash is to reduce the amount of water in the effluent spent wash as much as possible and as cheaply as possible. The water removed from the spent wash by either the evaporator or FO unit should be of the quality for operations or even potable water standards. Others have already described this source of water for use as operations and potable water suitable for drinking and boiler and solvent and cooling tower use.

[0054] Further advantages and improvements may very well be made to the present invention without deviating from its scope. Although the invention has been shown and described in what is conceived to be the most practical and preferred embodiment, it is recognized that departures may be made therefrom within the scope of the invention, which is not to be limited to the details disclosed herein but is to be accorded the full scope of the claims so as to embrace any and all equivalent devices and apparatus. Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of the common general knowledge in this field.

[0055] In the present specification and claims (if any), the word comprising and its derivatives including comprises and comprise include each of the stated integers but does not exclude the inclusion of one or more further integers.

2018100802 15 Jun 2018

Claims

1. A method for concentrating juice or spent wash the method including the steps of:

(a) providing a juice for concentration;

2. The method of claim 1 where the evaporation process includes single or multiple evaporators in series.

3. A system for producing concentrated juice the system comprising:

4. The system of claim 1 where the juice is sugar cane juice or sugar beet juice or distillery spent wash.

1/2

2018100802 15 Jun 2018

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2018100802 15 Jun 2018

Figure 3

Life Cycle Cost per m³ of clean water reused ($) $28 $21

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