A method for recovering solid residue from waste liquor resulted from ethanol production through cassava fermentation

Technical Field

The present invention relates to a method for recovering solid residue from waste liquor resulted from ethanol production through cassava fermentation.

Technical Background

Cassava is one of the three major root and tuber crops in the world, and is the first choice for bio-ethanol production. By 2005, the planting area of cassava in China has already reached 6,570,000 Chinese acres, and there are more than 200 factories producing starch and ethanol from cassava in China, with annual starch production of 500,000 ton, and cassava-derived ethanol 250,000 ton. As waste liquor resulted from ethanol production through cassava fermentation contains high concentration of organic compounds, and the waste liquor is directly discharged from most ethanol factories without any effective treatment, local and downstream water environment is severely affected.

Presently, treatment methods of waste liquor resulted from ethanol production through cassava fermentation include: 1. incineration method, i.e. incinerating the waste liquor after concentration, which is likely to cause secondary pollution after incineration; 2. marsh gas production through fermentation of the waster liquor, which has the disadvantage of high investment and high requirement for control techniques.

Thus, presently the available treatment method of waste liquor resulted from ethanol production through cassava fermentation is to use solid residue recovered from the waste liquor as feed, which comprises removing water from the waste liquor by filtering to give filter cake, and then drying the filter cake. This treatment method has the advantage of low investment, simple operation, and environmental friendliness. But the method has high energy consumption, causes severe wearing to squeezing equipment due to high impurity content in water during filtering process, and thus leads to high maintenance cost. In addition, the removed water has high COD (chemical oxygen demand), and brings heavy burden to environment.

Summary of the Invention

The object of the present invention is to overcome the high energy consumption disadvantage in available methods for recovering solid residue from waste liquor resulted from ethanol production through cassava fermentation, and provides a method for recovering solid residue from waste liquor resulted from ethanol production through cassava fermentation which has low energy consumption.

The inventor of the present invention has done intensive research on the available methods for recovering solid residue from waste liquor resulted from ethanol production through cassava fermentation; and has found that the water content of the filter cake resulted from water removal of the waste liquor is usually 75wt% or higher, and the available methods can not further decrease the water content of the filter cake, which leads to high energy consumption in the subsequent drying process.

The present invention provides a method for recovering solid residue from waste liquor resulted from ethanol production through cassava fermentation, which comprises the steps of: removing water from the waste liquor to give a filter cake having a water content less than 60wt% based on the total weight of the filter cake; and drying the filter cake to obtain a solid residue.

The present invention significantly lowers energy consumption required in the subsequent drying process by dramatically reducing water content of the filter cake. For example, the filter cakes Al -A3 obtained in the examples 1-3 in the present invention respectively have water contents of 60wt%, 50wt%, and 55wt%, while the reference filter cake CAl obtained in the comparison example 1 has water content as high as 78wt%. Therefore, the inventive method filters and squeezes the waste liquor resulted from ethanol production through cassava fermentation to give filter cake with significantly lowered water content. Additionally, compared with the comparison example 1, the examples 1-3 have significantly reduced energy consumption for drying; therefore, the inventive method can dramatically reduce energy consumption required for recovering the solid residue.

Embodiments

The present invention provides a method for recovering solid residue from waste liquor resulted from ethanol production through cassava fermentation, which comprises the steps of: removing water from the waste liquor to give a filter cake having a water content less than 60wt% based on the total weight of the filter cake; and drying the filter cake to obtain a solid residue.

According to the present invention, the filter cake having a water content less than 60wt% can be obtained through various means, for example, by filtering and squeezing the waste liquor.

The inventor of the present invention has done intensive research on the available methods for recovering solid residue from waste liquor resulted from ethanol production through cassava fermentation, and has found that the available methods usually adopt common filter press for filtering the waste liquor. During filtering, the waste liquor enters the space between the common filter plates of the filter press, solid particles are trapped in space between the filter plates by the filter medium of the filter plate, while liquid passes through the filter medium and is discharged via outlet; with ongoing of the filtering process, thickness of the filter cake increases gradually, and resistance to the dehydrating multiples, which leads to dramatic decrease of treatment capacity; moreover, due to limitation of inherent properties of the common filter plate, filter pressure can not be further increased (usually below IMPa), and thus water content of the obtained filter cake can not be further decreased.

According to the present invention, various equipments can be used to filter and squeeze the waste liquor, and membrane filter press is preferably adopted. The membrane filter press has not only filtering function same as that of common filter press, but also squeezing function for further dehydrating filter cake. In the membrane filter press, common filter plate and membrane filter plate are alternately arranged, and the middle core plate and two side membranes of the membrane filter plate are tightly pressed to form two sealed sandwich layers. The membrane filter plate has the same filtering function as common filter plate, but additionally has squeezing function, i.e. after filtering is finished, squeezing medium is injected into the sealed sandwich layer via the inlet hole of the core plate, and the filtered filter cake can be swollen and squeezed for further dehydrating by the elastic action of the membrane.

The numbers of common filter plates and the membrane filter plates in the membrane filter can be adjusted according to the concentration of the waste liquor, and preferably, the number of the common filter plate is 50-60. The common filter plate can be purchased commercially, such as chamber filter plate manufactured by Jingjin Filter Press Group. The number of the membrane filter plates is preferably 50-60. The membrane filter plate can be purchased commercially, such as 1250-type membrane filter plate manufactured by Jingjin Filter Press Group. The common filter plates and the membrane filter plates are alternately arranged at number ratio of 1:1. The membrane filter press satisfying the aforementioned requirements can be commercially purchased, such as X _M ^A ZG600/1500 X 2000U ^B κ-type membrane filter press manufactured by Jingjin Filter Press Group.

The inventor of the present invention has found that the membrane filter press can not only significantly reduce water content of the obtained filter cake, but also dramatically decrease impurity content in water removed therefrom, so as to alleviate impurity-induced wearing to equipment and lower maintenance cost; and the COD of the removed water is low, such that impact on environment is lowered.

In the present invention, the waste liquor resulted from ethanol production through cassava fermentation refers to residual solid-liquid mixture resulted from ethanol distillation during ethanol production through cassava fermentation.

In the present invention, there is no special limitation on filtering conditions, preferably, the filtering conditions comprise filtering pressure of 0.4-1MPa, and filtering time of 2-8hr; more preferably, filtering pressure of 0.5-0.8MPa, and filtering time of 4-6hr.

According to the present invention, there is no special limitation on squeezing conditions, preferably, the squeezing conditions comprise squeezing pressure of 10-25MPa, and squeezing time of 0.2-2hr; more preferably, squeezing pressure of 15-20MPa, and squeezing time of 0.5- lhr.

In the present invention, the squeezing pressure can be realized by filling squeezing medium into the membrane filter press, and the said squeezing medium can be various common squeezing medium for membrane filter press, such as compressed air and/or water.

According to the present invention, the drying equipment can be various routine drying equipments, such as HZG-series dryer manufactured by Shenyang Yuanda Co. Ltd, and combined WJI-900B fluid-bed dryer and XLS-100 type flash dryer manufactured by Beijing Yimin Gongmao Co. Ltd. The drying conditions are well known to those skilled in the art, for example, the drying conditions include drying temperature of 100-200 ⁰ C, and drying time of 0.2-2hr, preferably, drying temperature of 120-150°C, and drying time of 0.5-lhr.

The present invention will be explained in further detail through the following examples.

Example 1

1 ton of waste liquor with water content of 95wt% resulted from ethanol production through cassava fermentation is charged into membrane filter press (Jingjin Filter Press Group, X _M ^A ZG600/1500 X 2000U ^B _K ) for filtering, wherein the membrane filter press has 50 common filter plates (Jingjin Filter Press Group, chamber filter plate), and 50 membrane filter plates (Jingjin Filter Press Group, 1250 Type) therein, and the common filter plates and the membrane filter plates are alternately arranged. Filter cake is obtained at the filtering conditions of filtering pressure 0.8MPa and filtering time 2 hr. After filtering process, air is charged as squeezing medium between the membrane filter plates for performing squeezing

on the filter cake at squeezing pressure lOMPa for 2hr to obtain filter cake Al.

The water content of the filter cake Al is determined by using moisture meter (SH-IOA, Shanghai Precision & Scientific Instrument Co. Ltd.), and the result is shown in Table 1.

The obtained filter cake Al is placed into airflow rotary drum dryer (JB/T10279-2001, Zhengzhou Wangu Machinery Co. Ltd.) for drying at 120 °C for 1.5hr to obtain solid residue Dl, the water content in the solid residue Dl is determined by using moisture meter (SH-IOA, Shanghai precision & scientific instrument Co. Ltd.), and the water content and drying energy consumption of the solid residue Dl are shown in Table 1.

The energy consumption refers to coal consumed for removing lkg of water via drying, with unit of kg/kg.

Comparison example 1

The waste liquor resulted from ethanol production through cassava fermentation is filtered by the same method as that in the embodiment 1, except that all the membrane filter plates (1250 type, Jingjin Filter Press Group) are replaced by the common filter plates (chamber filter plate, Jingjin Filter Press Group). The filtering conditions include filtering pressure 0.8MPa and filtering time 2hr, and reference filter cake CAl is obtained.

The water content of the reference filter cake CAl is determined by using moisture meter (SH-IOA, Shanghai Precision & Scientific Instrument Co. Ltd.), and the result is shown in Table 1.

The obtained reference filter cake CAl is placed into airflow rotary drum dryer (JB/T10279-2001, Zhengzhou Wangu Machinery Co. Ltd.) for drying at 120°C for 1.5hr to obtain solid residue CDl, the water content in the solid residue CDl is determined by using moisture meter (SH-IOA, Shanghai Precision & Scientific Instrument Co. Ltd.), and the water content and drying energy consumption of the solid residue CDl are shown in Table 1.

The energy consumption refers to coal consumed for removing lkg of water via drying, with unit of kg/kg.

Example 2

1 ton of waste liquor with water content of 95wt% resulted from ethanol production through cassava fermentation is charged into membrane filter press (Jingjin Filter Press Group, X _M ^A ZG600/1500 X 2000U ^B _K ) for filtering, wherein the membrane filter press has 60 common filter plates (Jingjin Filter Press Group, chamber filter plate), and 60 membrane filter plates (Jingjin Filter Press Group, 1250 Type) therein, and the common filter plates and the membrane filter plates are alternately arranged. Filter cake is obtained at the filtering conditions of filtering pressure 0.4MPa and filtering time 8 hr. After filtering process, air is charged as squeezing medium between the membrane filter plates for performing squeezing on the filter cake at squeezing pressure 25MPa for 0.2hr to obtain filter cake A2.

The water content of the filter cake A2 is determined by using moisture meter (SH-IOA, Shanghai Precision & Scientific Instrument Co. Ltd.), and the result is shown in Table 1.

The obtained filter cake A2 is placed into airflow rotary drum dryer (JB/T10279-2001, Zhengzhou Wangu Machinery Co. Ltd.) for drying at 180°C for 0.5hr to obtain solid residue D2, the water content in the solid residue D2 is determined by using moisture meter (SH-IOA,

Shanghai Precision & Scientific Instrument Co. Ltd.), and the water content and drying energy consumption of the solid residue D2 are shown in Table 1.

The energy consumption refers to coal consumed for removing lkg of water via drying, with unit of kg/kg.

Example 3

1 ton of waste liquor with water content of 95wt% resulted from ethanol production through cassava fermentation is charged into membrane filter press (Jingjin Filter Press Group, XM ^A ZG600/1500 X 2000U ^B K) for filtering wherein the membrane filter press has 55 common filter plates (Jingjin Filter Press Group, chamber filter plate), and 55 membrane filter plates (Jingjin Filter Press Group, 1250 Type) therein, and the common filter plates and the membrane filter plates are alternately arranged. Filter cake is obtained at the filtering conditions of filtering pressure 0.5MPa and filtering time 6 hr. After filtering process, air is charged as squeezing medium between the membrane filter plates for performing squeezing on the filter cake at squeezing pressure 20MPa for 0.5hr to obtain filter cake A3.

The water content of the filter cake A3 is determined by using moisture meter (SH-IOA, Shanghai precision & scientific instrument Co. Ltd.), and the result is shown in Table 1.

The obtained filter cake A3 is placed into airflow rotary drum dryer (JB/T10279-2001, Zhengzhou Wangu Machinery Co. Ltd.) for drying at 120 °C for 0.5hr to obtain solid residue D3, the water content in the solid residue D3 is determined by using moisture meter (SH-IOA, Shanghai Precision & Scientific Instrument Co. Ltd.), and the water content and drying energy consumption of the solid residue D3 are shown in Table 1.

The energy consumption refers to coal consumed for removing lkg of water via drying, with unit of kg/kg.

Tablel

It can be observed from the Table 1 that the water contents of the filter cakes A1-A3 obtained in the examples 1-3 are respectively 60wt%, 50wt%, and 55wt%, while the water content of the reference filter cake CAl obtained in the comparison example 1 is as high as 78wt%; therefore the filter cake obtained by filtering and squeezing the waste liquor according to the inventive method has significantly reduced water content. In addition, compared with the comparison example 1, the examples 1-3 have dramatically reduced energy consumption for drying, indicating that the inventive method can significantly reduce energy consumption required by recovery of the solid residue.

Examples 4-6

Impurity contents and COD values in water removed by squeezing in the examples 1-3 are respectively determined by the following methods:

Determination of impurity content

The determination method comprises stirring water removed by squeezing in the examples 1-3 well to form suspension, taking 1,00Og of the suspension, allowing it to stand for 24hr, removing the supernatant, and weighing the precipitate to obtain impurity content in the water removed by squeezing. And the result is shown in Table 2.

Determination of COD value

COD values of the water removed by squeezing in the examples 1-3 are respectively determined by Chinese National Standard GB11914-89 Water quality-Determination of the chemical oxygen demand-Dichromate method. And the result is shown in Table 2.

Comparison example 2

The impurity content and COD value of the removed water in the comparison example 1 is determined according to the methods same as those in the examples 4-6. And the result is shown in Table 2.

Table 2

It can be obtained from the Table 2 that compared with the removed water obtained in the comparison example 1, the water removed by squeezing in the examples 1-3 has significantly lower impurity contents and COD values, indicating that the inventive method can not only significantly reduce energy consumption required for recovery of the solid residue, but also dramatically lower impurity content and COD value of water removed by squeezing, so as to reduce impurity-induced wearing of equipment, lower maintenance cost, and reduce adverse impact on environment.