International Sugar Journal

“E-max” design technology for process efficiency and optimum energy economy in molasses/grain based ethanol plants

Abstract

Over the last three decades potable alcohol and biofuel sectors have advanced enormously. Technological progress has supported process efficiency, energy economy as well as water conservation and achieving zero effluent discharge. With reference to case studies, this paper highlights productivity gains of various molasses and grain based ethanol plants recently engineered and built by Excel Engineers & Consultants compared with the industry norms.

Introduction

Excel Engineers & Consultants based in Pune India has more than 20 years of experience in providing technology solutions in the field of distillery, biofuels, zero liquid effluent discharge plants and renewable energy.  Excel offer services right from concept to commissioning with modern plants custom build to meet individual client’s requirements. Excel has pioneered plant designs and implemented technologies to reduce energy consumption reduce on effluent generation and increase efficiencies.

Excel’s quest to search for cost effective, energy efficient and novel processes and engineering solutions resulted in the development of in house “E-max” Technologies.

Holistic approach is of utmost importance during conceptualization of new grain / molasses distillery projects. In present condition, many of the distillery units are struggling to achieve technical and economic efficiencies due to mismatch in the process requirements, utilities and effluent treatment methods. Later on, de-bottlenecking at such distillery units becomes a critical and costly affair. Hence; a complete Heat Mass Balance should be taken into consideration while conceptualizing a distillery project.

Recently, Excel got the opportunity to work with many of distilleries such as Globus Spirits Ltd., Chandigarh Distilleries & Breweries Ltd., Rana Sugars Ltd., IFB Agro Ltd, EID Parry Ltd., NSL Krishnaveni Sugars Ltd., Madhucon Sugars & Power Industries Ltd.and Tikaula Distilleries in India.  At these units, Excel carried de-bottlenecking to drive energy efficiency, zero effluent discharge and ultimately, increased profitability. .

Excel’s new projects are conceptualized for maximum efficiencies at optimum utility requirements. These projects are modern and progressive in terms of the technology for heat integration.

Grain distilleries

A typical grain distillery essentially consists of grain receiving and pre-cleaning station, grain storage silos, grain handling, cleaning, milling, floor handling and storage, enzymatic liquefaction, saccharification and fermentation, distillation, decantation and evaporation, DWGS (distillers wet grain solubles) mixing and handling, DDGS (distillers dry grain solubles) drying and bagging, cogeneration plant, water treatment and effluent treatment plants.

Case study – CDBL, Punjab and Globus Spirits Ltd India

During 2012-13, Excel designed, delivered and commissioned India’s largest 300,000 litres/day multi-feed (grain + molasses) distillery at CDBL, Punjab and immediately got opportunity to modernize existing grain distilleries of Globus Spirits Ltd. With technical modifications in existing traditional facility, the steam consumption for total grain distillery complex (including liquefaction, ENA distillation, thin slop evaporation and DDGS Dryer) was brought down from 6.5 kg/litre to 4.5 kg/litre of spirit production. Fresh water requirement for overall distillery complex was also reduced by 20 to 25%. The DDGS dryer supplied by Excel easily ensured 100% concentrated syrup utilization and thereby high protein content in DDGS product. The innovation was not limited and Excel integrated thin slop evaporation plant to run on Dryer vapours. As recognition from client, Excel got selected as a technology partner for turnkey 100,000 litres/daygrain distilleries at West Bengal and 80,000 litres/day grain distillery at Bihar by Globus Spirits Ltd.

Table 1 highlights productivity improvements at various grain distilleries following intervention by Excel.

Table 1. Redefined efficiencies and performance benchmarks in grain distilleries

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The performance benchmarks are certainly beyond the regularly achieved parameters in distillery industry. Hence; along with CDBL and Globus Spirit Ltd., Excel is now chosen by major grain distilleries in India such as Rana Sugars Ltd., Oasis Group, Haryana Liquors, IFB Agro Ltd., Madhucon Sugars Ltd. and Jagruti Bio Ltd, Sentini Bio-products Ltd.

Molasses distilleries

Excel many clients in the molasses-based potable and fuel ethanol distilleries sector include NSL Krishnaveni Sugars Limited, Telangana, Sai Priya Sugars Limited, Karnataka for their 120,000litre distillery, 60,000 litres/day molasses distillery at MRN Cane Sugars Limited, Karnataka, Tikaula Distilleries Ltd, Uttar Pradesh, Rana Sugars Ltd, Punjab, KM Sugars, San Carlos BioFuels, Philippines and Om sugars.

Case study – NSL Krishnaveni Sugars Limited, Telangana, India

NSL Krishnaveni Sugars Limited @16.3015738, 77.919277 is situated at Ramakrishnapur, Kothakota Mandal, Mahabubnagar, Telangana State, India. In 2015, Excel built a modern 60,000 litres/daymolasses based ethanol plant on “E-max” Technology at NSL Krishnaveni Sugars Limited, Telangana, India (figures 1 and 2). The plant was built from concept to commissioning in a record time of 6 months and 21 days and performance parameters were achieved during first run itself. The total ethanol project consists of molasses bulk storage tanks for storage of in-house and procured molasses, molasses weighing system, fed-batch mode fermentation plant, multi-pressure primary distillation plant along with integrated falling film type evaporators, combination of falling film and forced circulation type evaporation bodies in standalone evaporation, molecular sieve dehydration plant based on pressure swing adsorption technology, ethanol storage tank farm etc. The effluent spent wash generated from distillation is concentrated upto 60% w/w solid concentration and then incinerated in boiler along with coal as an auxiliary fuel. The total ethanol manufacturing facility is designed for achieving maximum utility economy, lowest cost of production, high efficiencies and zero liquid effluent discharge. 

Figure 1. 60,000 litres/day ethanol plant built by Excel for NSL Krishnaveni Sugars  

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Figure 2. Overall mass balance – 60,000 l/d molasses based ethanol plant at NSL Krishnaveni Sugars Ltd.

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Fermentation plant

The fermentation plant has 4-fermentor system with flexibility of operating in synchronized as well as fed batch modes. Yeast propagation is done in culture vessels. A wash settling system and sludge separation system is also employed for removal of suspended solids from fermented wash. Fermentation vessels construction ensures process hygiene and homogeneity of fermented wash. Every fermentor tank is provided with wash circulation cum transfer pumps, plate heat exchangers for efficient wash temperature control, 3600 CIP cleaning nozzles, safety system and tapping for CO2 recovery. CO2 generated during process is scrubbed with water to recover alcohol traces and it is then taken to CO2 plant for producing liquid CO2 and dry ice. Alcohol concentration in fermented wash is consistently maintained at 10.5 % v/v and fermentation efficiency is 91%.

Multi-pressure distillation and integrated evaporation plant

Fermented wash at 9 to 11% v/v alcohol concentration is fed to Primary Column which is operated under vacuum. Non condensable gases in fermented wash are removed in degasifying column which operates on primary column partial vapors. Aldehydes are removed in de-aldehyde column. Rectifying cum exhaust column operates under pressure and driven by medium pressure steam at 3.5 kg/cm2 (g) and temperature 1480 C. High enthalpy contained in rectifier column vapors is utilized to operate primary column through thermo-siphon reboilers. Higher and lower fusel oil streams are fed to fusel oil concentration column to recover fusel oils. Three effect falling film type evaporators are integrated on primary column vapors (figure 3). Raw spent wash from primary column bottom comes out at 840 C and fed to integrated evaporation plant. Integrated evaporation plant is operated under vacuum.

Figure 3. Heat-mass balance for multi-pressure distillation and integrated (first stage) evaporation plant

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Standalone (second stage) evaporation plant

Partially concentrated spent wash is fed to a stand-alone second stage evaporation plant (figure 4). This plant consists of three falling film type evaporators and one forced circulation type body. One more force circulation type evaporation body is provided as a standby to last forced circulation type body. This is to ensure periodic operation switch over and automatic cleaning of evaporation body and thereby extending the operation days of evaporation plant without any stoppage on account of cleaning. All the evaporation equipment including calendrias, tubes, tubesheets etc. are provided in SS316 construction for long plant life. The system is operated under vacuum and optimum heat integration is done to ensure low steam consumption.

Figure 4. Heat-mass balance for standalone (second stage) evaporation plant

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Molecular sieve dehydration plant

Absolute alcohol plant employs molecular sieve dehydration technology. This fuel ethanol plant works on pressure swing adsorption technique and employs crystalline, hydrated metal alumino silicate adsorbent material with uniform pore diameter which is thermally stable higher temperatures (figure 5). Rectified spirit of around 95% v/v strength is fed to this plant and fuel ethanol with 99.9% v/v strength is obtained.

Figure 5. Heat-mass balance for molecular sieve dehydration unit

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Actual electric power consumption

Optimum electric power consumption is a prime criteria in the design of an ethanol plant. Even if there is more hardware provided and more operating pumps for achieving maximum heat integration, the power consumption is low in Excel designed units compared to existing molasses distilleries in India (Table 2).

Table 2. Actual power consumption at NSL Krishnaveni Sugars Ltd- ethanol plant.  

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The plant was successfully commissioned in April 2016. Table 3 shows the actual production and operating performance parameters achieved in the months of June, July and August 2016.

Table 3. Performance parameters at the 60,000 l/d distillery at NSL Krishnaveni Sugars Ltd.

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Table 3 shows that the ethanol plant has been operating at 110% capacity during June-August 2016. Regarding energy economy, the overall steam consumption including primary distillation, fuel ethanol plant and evaporation upto 60% w/w solid concentration is around 2.75 kg/litre of fuel ethanol as compared to 4 to 4.5 kg/litre in available distillation and evaporation technologies in traditional distilleries. Final spent wash concentration of 60% w/w is consistently achieved and process efficiencies are also best in the industry.

Table 4 highlights productivity improvements at Molasses Based distilleries following intervention by Excel. It should be quite apparent that the gains are across process, energy economy and water use.

Table 4. Redefined efficiencies and performance benchmarks in molasses distilleries

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Conclusion

The ethanol plants built with Excel’s “E-max” Technologies have redefined the efficiencies, quality norms and performance benchmarks in fuel ethanol potable alcohol sectors. which have supported both significant productivity and financial gains for our clients running grain or molasses distilleries.