METHOD FOR CARRING OUT THE COMBINED OPERATION OF A BIOETHANOL PRODUCTION UNIT AND A BIOGAS UNIT

Abstract

The present invention concerns a method for carrying out the combined operation of a bioethanol production unit and a biogas unit. The method comprises the following steps: a) mashing corn meal from a dry milling step with at least 0.1 t of dry matter in the form of whole stillage and at least 0.1 m.sup.3 of outflow from the biogas unit per tonne of corn meal, b) feeding the mash from a) to a cooking stage with mash temperatures below the gelatinization temperature of the starch inn the corn meal, followed by an ethanol-forming fermentation step and then feeding the fermented mash to a distillation step, c) feeding the whole stillage from b) to the mashing step in a) and to the biogas unit.

Claims

1. A method for carrying out the combined operation of a bioethanol production unit and a biogas unit, wherein: a) corn meal from a dry milling step is mashed with at least 0.1 t of dry matter in the form of whole stillage and at least 0.1 m3 of outflow from the biogas unit per tonne of corn meal, b) the mash from 1a) is fed to a cooking stage with mash temperatures below the gelatinization temperature of the starch in the corn meal, followed by an ethanol-forming fermentation step and then feeding the fermented mash to a distillation step, the whole stillage from 1b) is fed to the mashing step in a) and to the biogas unit.

2. The method as claimed in claim 1, wherein at least 0.2 t TS per tonne of corn meal is added to the mashing step in 1a) in the form of a mixture of thin stillage and whole stillage.

3. The method as claimed in claim 1, wherein at least 0.12 t TS per tonne of corn meal is recycled to the mashing step in 1a) in the form of whole stillage.

4. The method as claimed in claim 1, wherein at least 0.1 t TS of thin stillage per t of mash is recycled to the mashing step in 1a).

5. The method as claimed in claim 1, wherein the cooking stage in 1b), the mash is heated to a maximum of 70° C.

6. The method as claimed in claim 1, wherein the corn meal in 1a) from a dry milling step has a mass fraction of at least 60% of particles with a particle size of <0.5 mm.

7. The method as claimed in claim 1, wherein the pH of the mash in 1a) is adjusted to less than 4.5.

8. The method as claimed in claim 1, wherein the ammonium nitrogen content in the biogas fermenters of the biogas unit is kept at between 6000-9000 ppm.

9. The method as claimed in claim 1, wherein the mean hydraulic residence time for the biogas unit is at least 30 days.

10. The method as claimed in claim 1, wherein the proportion of outflow from the biogas unit per tonne of corn meal in 1a) is at least 0.2 m.sup.3.

11. The method as claimed in claim 1, wherein the distillation step in 1b), at least 400 liters of ethanol are separated per tonne of corn meal.

12. The method as claimed in claim 1, wherein the mashing step in 1a), at least 100 g of ammonium nitrogen per tonne of corn meal is recycled via the outflow from the biogas unit.

13. The method as claimed in claim 1, wherein the mashing step in 1a), a maximum of 1000 g of ammonium nitrogen per tonne of corn is recycled via the outflow from the biogas unit.

14. The method as claimed in claim 1, wherein less than 1.2 m.sup.3 of fresh water is used per tonne of corn meal.

15. The method as claimed in claim 1, wherein at least 15 kg of glycerin per tonne of corn meal is recycled to the mashing step via the whole stillage and thin stillage.

16. A method for carrying out the combined operation of a bioethanol production unit and a biogas unit, wherein: a) corn meal from a dry milling step is mashed with at least 5 kg of cellulose in the form of whole stillage and at least 0.1 m.sup.3 of outflow per tonne of corn meal from the biogas unit, which latter contains cellulases and/or cellulase-producing microorganisms, b) the mash from 1a) is fed to a cooking stage with mash temperatures below the gelatinization temperature of the starch in the corn meal, followed by an ethanol-forming fermentation step and then feeding the fermented mash to a distillation step, the whole stillage from 1b) is fed to the mashing step in 1a) and to the biogas unit.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0066] The invention will now be described in more detail with the aid of two exemplary embodiments and associated drawings, in which:

[0067] FIG. 1 and FIG. 2 diagrammatically describe the process workflow for embodiments in accordance with the invention.

EXEMPLARY EMBODIMENT 1

[0068] FIG. 1 shows a diagrammatic representation of the method without the production of animal feed, foodstuffs and corn oil. Table 1 shows the composition of the corn meal for this exemplary embodiment. Table 2 shows the mass flow rates for this exemplary embodiment.

[0069] Step 1: Corn is fed to a dry milling step. The corn has a mass fraction of 60% of particles of less than 0.5 mm and a TS content of 85%.

TABLE-US-00001 TABLE 1 Corn meal composition Mass fraction of original substance (OS) Mass fraction of TS Water 15.00% Starch 60.90% 71.65% Sugar 2.20% 2.59% Protein 8.10% 9.53% Fat 3.70% 4.35% Lignocellulose 8.90% 10.47% Ash 1.20% 1.41% Total 100.0% 100.0%

[0070] Step 2: 1.0 t/h of corn meal is mashed with 0.4 t/h of outflow from the biogas unit, 0.8 t/h of whole stillage, 1.6 t/h of thin stillage and 0.46 t/h of process liquid from the ethanol unit and 0.12 t/h of water (for example drinking water). The outflow from the biogas unit, whole stillage, thin stillage and process liquids, has TS contents of 4%, 20.5%, 15% and approximately 0%. Thus, per tonne of corn meal, approximately 0.4 m.sup.3 of outflow from the biogas unit, 0.16 t TS of whole stillage, and 0.4 t TS of mixed stillage (whole stillage and thin stillage) is fed to the mashing step. The outflow from the biogas unit has a NH4-N concentration of 500 ppm. In this regard, 200 g of NH4-N in the form of outflow from the biogas unit per tonne of corn meal is fed to the mashing step. The pH is adjusted to 4.2 using sulfuric acid and enzymes for digesting the starches are added (not shown in FIG. 1 and the mass balance of Table 2).

[0071] Step 3a: The mash from step 2 is fed to a cooking stage and heated to 60° C.

[0072] Step 3b: The mash from step 3a is cooled to below 30° C. Glucoamylase and yeast are added (not shown in FIG. 1 and mass balance of Table 2) and starch is converted into ethanol in the fermentation step.

[0073] Step 3c: The ethanol-containing mash is fed to a distillation step at 67° C. and 0.344 t/h of ethanol is removed from the mash (corresponds to 436 liters per tonne of corn meal). The stream of ethanol is freed from water in further steps and the stream of water is fed to the mashing step as the process liquid. The ethanol-depleted mash, the whole stillage, from the distillation step is fed to the mashing step at 0.8 t/h (step 2), to the biogas unit at 0.14 t/h (step 5) and to the solid-liquid separation step at 2.3 t/h (step 4).

[0074] Step 4: 2.3 t/h of whole stillage from step 3 undergoes a solid-liquid separation step in a decanter centrifuge. This produces thin stillage and wet cake. The thin stillage is recycled to the mashing step (step 2); the wet cake is fed to the biogas unit (step 5).

[0075] Step 5a: Whole stillage from step 3 and wet cake from step 4 and 0.14 t TS/h of wheat straw are fed to the biogas fermenter of the first stage. The outflow from the biogas fermenter of the first stage is fed to the biogas fermenter of the second stage. The outflow from the biogas fermenter of the second stage is fed to the biogas fermenter of the third stage. Biogas is produced in all three stages. 1.3 MW of biogas is formed in the entire biogas unit. The mean hydraulic residence time for the biogas unit as a whole is 70 days.

[0076] Step 5b: The outflow from the biogas fermenter of the third stage of step 5a is fed to a decanter centrifuge of a solid-liquid separation step. Outflow solids are thus formed which are discharged from the biogas unit.

[0077] Step 5c: The liquid phase from step 5b is fed to an ammonia stripping step (ammonium removal). Here, ammonia is removed from the liquid phase and the NH4-N content falls to 500 ppm. The ammonium which is removed is discharged from the biogas unit in the form of ammonium sulfate. 0.4 t/h of outflow with a 500 ppm NH4-N content was fed to the mashing step (step 2). A portion of the outflow was recycled to the biogas fermenter in step 5a, in order to adjust the NH4-N concentration in the biogas fermenter to 6000-9000 ppm. The concentrations of organic acids and aromatic compounds in the outflow from the biogas unit is a maximum of 150 ppm respectively.

[0078] Energy balance: The biogas which is obtained from the biogas unit covers the entire energy requirement for the combined bioethanol and biogas unit. For the fuels produced, this means that the CI score is significantly improved compared with a typical bioethanol unit. In a typical bioethanol unit, the energy consumptions increase the CI score by approximately 20-25 gCO.sub.2e/MJ.

[0079] Water consumption: The freshwater requirement for the unit is only approximately 0.1 m.sup.3 per tonne of corn meal, which corresponds to a reduction in fresh water by one order of magnitude compared with a typical bioethanol unit.

TABLE-US-00002 TABLE 2 Mass flow rates for Exemplary embodiment 1 t/h t TS/h Parameters Dry milling (step 1) Corn maize, in ~1 ~0.85 Corn meal to step 1 1.00 0.85 Mashing (step 2) Corn meal from step 1 1.00 0.85 Biogas unit outflow from 0.40 0.02 ~0.4 m.sup.3 per t corn meal step 5 Whole stillage from step 3 0.80 0.16 0.16 t TS whole stillage per t corn meal Thin stillage from step 4 1.60 0.24 Mixed stillage (whole stillage 2.40 0.40 0.40 t TS mixed stillage and thin stillage, calculated) (whole stillage and thin stillage) per t corn meal Process liquid 0.46 ~0 Water 0.12 ~0

Exemplary Embodiment 2

[0080] FIG. 2 shows a diagrammatic representation of the method with the production of high added value, protein-rich animal feed and foodstuffs and corn oil.

[0081] Step 1a: Corn is fed to the ethanol production step. This contains the process steps of dry milling, mashing, fermentation, distillation and solid-liquid separation of a portion of the whole stillage. Process water is fed in the form of blowdown water from the cooling water system and blowdown water from the steam production system, as well as outflow from the biogas unit. The products are ethanol and carbon dioxide, and whole stillage, wet cake and thin stillage as intermediate products.

[0082] Step 1b: High added value, protein-rich animal feed and foodstuffs as well as corn oil are obtained as products from the thin stillage from step 1a. In this regard, “protein-rich” means that the raw protein content (mass fraction of protein in TS) with respect to the thin stillage has been increased using suitable processes. Residual substances are obtained as intermediate products and have a lower raw protein content than the thin stillage.

[0083] Step 2a: Whole stillage and wet cake from step 1a as well as residual substances from step 1 b are fed to the biogas fermenters. Biogas fermenter outflow as well as biogas are obtained as intermediate products.

[0084] Step 2b: The biogas from step 2a is used for the production of process energy (steam, electricity) and/or are fed to a biogas purification step in which biomethane and carbon dioxide are obtained as products.

[0085] Step 2c: The biogas fermenter outflow from step 2a is fed to an outflow purification step. In a solid-liquid separation step, an outflow solid is produced as a product which, for example, could be used as a high added value fertilizer and soil improver. The liquid phase is fed to an ammonia stripping step in which an ammonium salt, optionally as an ammonium salt solution, is obtained as a product. The ammonium-depleted, liquid phase is fed to an evaporation step in which a nutrient concentrate is obtained as a product which, for example, could be used as a fertilizer. An outflow with a reduced nutrient, ammonium and solids fraction compared with the biogas fermenter outflow is obtained from the condensates from the evaporation step as an intermediate product.

[0086] Energy balance: Depending on the quantity of corn oil and animal feed/foodstuffs produced, the biogas produced in the biogas unit may be sufficient to cover the entire energy requirement for the combined ethanol unit and biogas unit. External energy sources might be necessary.

[0087] Water consumption: The freshwater requirement for the unit is only approximately 0.1 m.sup.3 per tonne of corn meal, which corresponds to a reduction in fresh water of about one order of magnitude compared with a typical bioethanol unit.

BIBLIOGRAPHY

[0088] Jacques, K., Lyons, T., & Kelsall, D. (2003). The Alcohol Textbook 4.sup.th Edition. Nottingham, United Kingdom: Nottingham University Press. [0089] Victor Guadalupe Medina, Marinka J. H. Almering, Antonius J. A. van Maris, Jack T. Pronk. Applied and Environmental Microbiology December 2009, 76 (1) 190-195; DOI: 10.1128/AEM.01772-09. [0090] Mueller, S., 2010b, Detailed Report: 2008 National Dry Mill Corn Ethanol Survey, Energy Resource Center, University of IL at Chicago, May. [0091] Walker, G., Abbas, C., Ingledew, W., & Pilgrim, C. (2017). The Alcohol Textbook 6.sup.th Edition. Duluth, Ga., USA: Lallemand Biofuels & Distilled Spirits.