Process Plant Design

Detail design of Mixer: Guide

2021-05-23T09:00:00.000-07:00

Besides dimension of the vessel, impeller and baffles certain physical data are needed for complete description of slurry mixing problem

1. Specific gravities of solid and liquid

2. Solid content of the slurry (wt %)

3. Settling velocity of the particles (ft/min)

Design duty

1. Design conditions: Slurry properties

Volume=1000gal h/d=1

viscosity =1.7pa.s Mean particle size of solid=410 mm=0.0013ft

S1: Density of solid =1370.65kg/m³

S2: Density of liquid _{(0.5M Nacl})=1054Kg/m³.[6]

2. Fraction of the solids=15%

3. Settling velocity

Stokes law

Us = 9.97*10⁶ (S₁-S₂) D²/viscosity

= 9.97*10⁶*(1.370-1.054)(0.0013) ²/1.7

= 3.13ft/min

Consider the following mixer arrangement.

Final Project Ideas: Biomass fired circulating fluidized bed design, Pa...

2011-11-05T08:32:00.000-07:00

6 Parts detail design of Circulating Fluidized Bed

Final Project Ideas: Biomass fired circulating fluidized bed design, Pa...:
Introduction Today most of electrical or thermal energy is generated using non renewable energy sources. Their price is highly volatile and...

Here are the 6 parts

Related posts
Market study in plant design with example
Material & Energy balance example: Spray Drier

Material & Energy balance example: Spray Drier

2011-11-01T03:18:00.000-07:00

In the previous blog, material and energy balance in process design, I revised common principles of mass and energy balance. Balances on spray driers, kilns, furnace and filters has been described briefly. In this blog, I will describe the details of spray drier mass and energy balance.

The figure below shows the components of a spray drier system configuration. Drying air is first heated in the heater to the desired temperature as determined partly by the product property.The material to be dried is sprayed by spray system( nozzles) into the drying chamber. The dried product is collected by product
recovery system (cyclones). The air is recycled by blower back to the air heater.

Suppose 5.02kg/min of protein isolate, 60% solids at temperature of 15degreeC is to be dried to final specification of 93% protein and 5% moisture at 35degreeC. The amount of dry air should be determined from air heater energy balance but the final temperature can be assumed to be equal to the product temperature.

Mass balance

5.02=Mp+Mw

Solid balance

0.6*5.02=0.93*Mp

Mp=3.24Kg/min

Thus, mass flow rate of water in the product

Mw=0.05*3.24

=0.162Kg/min

Energy balance

Assume 10% heat gained on the heater is lost

m_a Air heater

T=25^oC ----------------------------> 100^oC

H=.013kg/kg dry air H=0.013kg/kgdry air

h=70.01kj/kg h=135.5kj/kg

where H is the relative humidity and h is the enthalpy

Heat gained by air on heating from 25-100^oC is

Q = m_a (135.5-70.01)

= 65.5*m_a

E_in= E_out + E_loss

_{Energy in, consists of the enthalpy of the feed(Ef) and the drying air (Eia) while energy out is the sum of the air out(Eoa), the enthalpy of the dried product(Ep) and latent heat of vaporization of water.(Revap)}

E_f+Eⁱ_a= E^o_a+E_p+R_{evap ..................................EQ. 1}

E_f=5.02*C_f*(288-273) feed at 15C

Eⁱ_a=Cⁱa*mⁱ_a*(373-273) air at 100C

E_p=C_p*m_p (323-273) product at 35C

E^o_a=Co_a*mⁱa (323-273) air at 35C

R_evap=lambda*m^o_w

Now lets determine the properties

C_p protein=2.0082+1.2089*10^-3*T - 1.3129*10^-6*T²

C_p at 15^oC=2.026 kJ/kg.^oK

35^oC=2.0486 kJ/kg.^oC

Specific heat capacity of air

C_a=1.005+1.88*H

H_i=0.0013 kg/kg dry air at 25^oC

Assume the relative humidity of the out let air to be 0.032kg/kgdry air. It can be checked back using water balance

Therefore C_pⁱ_a=1.02944kj/kg °C C_p^o_a=1.06516KJ/kg.oc

Substituting in the above energy balance equations,

E_f=5.02*2.026*(288-273) =152.55 kJ/min

Eⁱ_a=Mⁱ_a*1.0294*(373-273) =102.94*mⁱ_a

E_p=2.04*3.24*(323-273) =330.48 kJ/min

E^o_a=1.06516*m^o_a*(323-273) =53.25*m^o_a

R_evap=2360*0.162=382.32 kJ/min

E_loss=0.1*65.5*m^oa=6.55*m^o_a

The amount of air required for the drying process is not known initially. The air leaving the dryer is also not known. So as initial iteration we will assume they are equal. Since the relative humidity of the out let air has been assumed initially, it will be recalculated back and the iteration continues until the relative humidity calculated is equal to assumed.

mⁱ_a=m^o_a

Using equation 1, after substituting the calculated values

152.55+102.94*mⁱ_a=330.48+53.25*m^o_a+382.32+6.55*m^o_a

(102.94-53.25-6.55) moa=712.8

m^o_a=16.5 kg/min

Total amount of air (dry +moisture)

mia=16.5+0.013*16.5=16.71 kg/min

Total amount of air from drier,

(previously we calculated the amount water in the product is Mw=0.162 kg/min)

=16.71+0.162=16.87 kg/min

Amount of water in the air at the out let = Amount of water in the inlet air + amount of water evaporated

16.5*0.013+0.162= 0.377 kg/min

Relative humidity of exit air

3.0995/101.5 = 0.023 kg/kg dry air
This value is lower than the assumed 0.032, thus, more iterations are required.

From psychometric chart specific volume of air=1.075m³/Kg dry air

Therefore volumetric flow rate=1.075*16.5=17.74 m³/min it is recycled to the fresh air to reduce fresh air requirement. The final answer depends on the the value of m^o_aat the end of the iteration.

The overall thermal efficiency

h=T₁-T₂/ (T₁-T_o)*100

From psychometric chart, the corresponding to saturated condition of out let temperature of air at 25^oC

h=100-35/ (100-25) =87%

Therefore we can say that the design is good

I hope it is clear enough. If you have questions please leave them in the comment box or contact me. Please subscribe if you would like to get email updates of more balance and design examples.

Material and energy balance in process plant design

2011-10-31T09:23:00.000-07:00

Once the literature survey in done and the specific objectives and the plant size has been determined from demand study, the next step is to do the mass and energy balance. This is a crutial step as it affects the sizing and thus the economics of the plant.

In this blog, I will revise some principles and state how to do balances on filters, distillation columns, kilns and so on. Soon I will add more posts on solved energy and material balances on some key processes. Please subscribe to get email updates on the coming posts which you shouldn´t miss.

The market demand study and raw material availability studies give us the proper size of the manufacturing plant. The size of the plant should balance the raw material availability and the market demand. Based on this, the material and energy balances are done.

Using the information form demand study determine the capacity of the plant in terms of total annual production or total raw material requirement. This leads to the following ways of making balances.

There are two approaches for performing material and energy balances; upstream and downstream ways as known informally. In the upstream the balance is started from the last

unit in the process. Final product amount, quality, yield and equipment efficiency are mainly used to do the balance. In the downstream way, the initial raw material amount is determined to arrive at desired production capacity. This could be possible if the overall yield of the process in tons of product per tons of raw materials is known.

While writing material balance, the best format is to first present the overall or general material balance and second the component balance. Show clearly the total flow rate and composition of the known streams and represent the unknown stream with appropriate labels. At the end of each section prepare summary tables with columns input, output and remark. In the remark write balanced, or state the accumulated, generated or lost amount.

Balances for units with no change in mass like storage tanks are not done and it is acceptable. Electrical energy required for running units are not usually included in the balances. This is partly because their rating in only known in the sizing and at the end it is included in calculation of utility costs as fraction of total costs.

Choose the reference temperature to be the ambient conditions for energy balances. Always study the detail process steps before calculating the total energy requirement. Spray driers, kilns, coolers and combustion devices are included in this category and are always challenging. The common mistake is considering only sensible heat changes. The above units combine sensible, latent heat and super heating. Besides the processes are of simultaneous mass and heat transfer.

If you are dealing with mixtures in energy balance stream the overall physical properties like density, specific heat capacity and so on may be not found in tables. In this case they should be calculated based on the methods discussed in Coluson and Richardson, chemical engineering, Vol 6.

Balances of size reduction machines

Crushers, grinders and milling machines need mass balances in principle. Usually the dust loss and the recycled coarse fraction are ignored. This is not accurate and the best way to do this balance is to consider the grinder alone then balances for dust recovery cyclones (high efficiency or high throughput). If the control volume include the dust recovery system, it is possible to neglect the dust loss lost but still there is some loss. Wet grinding avoids the need for dust recovery systems. Since water is added during the crushing process the material balance should include this amount.

Energy balance for this units determines the energy required for crushing( Bond´s Law). But this is not relevant from energy balance point of view and is needed if it is designed in detail. This is because the energy required is usually calculated indirectly as utility cost. For more details see references 1 and 3.

Balances on filters

The filtration objective, whether the cake or the liquid is the final product, determines the type of filtration to be used and operating pressure. Overall balance on filters requires the calculation of the accumulated cake amount. This calculation intern requires pre-hand determination of the filter area, cake properties and operating pressures. Further complexity arises when the rate of filtrate flow should be determined for subsequent balances. This means the filter design and operation should be known pre-hand.

The best way to approach this problem is first to seek for general guides on operations of filtration units. See reference 11, which contains design guides such as cake properties of some common materials and performance data of filters. available.

Balances on spray driers

In spray driers hot air at given humidity and temperature absorbs moisture from wet substance and at the same time the heat is transferred. Hence both mass balance and energy balance equations should be used. The heat transferred raised the temperature of the dry air and the moisture. One typical problem is the final humidity of the exit air. It should be assumed to calculate the outlet air mass flow and solve the energy balance equations. Therefore some iteration is required to arrive at final values. For more details see reference 7.

Balances on kilns

Cement kilns balances are complex. The feed materials contain surface water and inherent water. The surface water undergoes sensible heat change and latent heat change at lower temperature. The inherent water in clay for instance, is evaporated in the kiln zone where temperature around 600C. Sensible heat change of every feed material should be considered. Besides separate balances of the primary and secondary kiln air should be done. Reaction energy of clinker formation reactions should be calculated. This calculation requires the knowledge of heat of formation of the kiln reactions at standard temperature and then at the kiln temperature. There is also considerable kiln gasses released as loss.

Useful references

1. Nicolas et al,2003, Hand book of chemical engineering calculations, McGraw Hill

2. Reynolds et al, 2002, Handbook of chemical and environmental engineering calculations,

3. Mc Cabe, Unit operation of chemical engineering, 3rd ed, Mc Graw Hill

4. Fundamentals of chemical engineering text book

5. Seader et al, 2^nd ed, Separation process principles, Willey

6. Chrome balance in leather processing http://www.4shared.com/document/2CzAlvHr/Chrome_balance_in_Leather_Proc.htm

7. Spray drier balances, G V Barbosa et al, 1997, Food engineering lab manual,

8. Mass balances in leather processing

http ://preresi .ineti .pt /documentacao /guias /doc _tec /Curtumes /UNIDO /MassBalance inLeatherProcessing .pdf

9. Online steam tables and unit converters www .cheresources .com

Online steam tables calculator, http ://www .dofmaster .com /steam .html

Critical reading in literature survey

2011-10-30T10:38:00.003-07:00

A literature survey is not a collection of paraphrases from many sources instead it is a serious evaluation of previous researches with an aim to expand on the reasons for pursuing a particular research.

It is important to be critical while reviewing literature in research investigation because of three main reasons. First, to develop properly the research questions and develop once own approach. Secondly, to know most important issues and their relative contribution to the research. Thirdly, to write papers critically.

Critical reading and thinking during literature review helps to establish a theoretical framework and methodological focus for a research. Especially if the research is new, a critical literature review helps to design a proper methodology relative to what has been done before. Being critical helps us know how the research is done than looking only at what has been achieved. Additionally in critically reviewing literature, the genuine difference between theories is observed. Being critical also allow to see where evidence is lacking and areas that need further test. These judgments and interpretations are the stepping stones towards designing an approach.

Critical reading of literature in research determines issues of high importance, potential controversies and the gap the research is going to fill. Additionally, we can determine where the research is heading and what is being neglected. It helps to determine significance and contributions made by researchers and the limitations of a particular study. Being critical during literature review contributes well to develop research question heading to proper direction while being aware of the value it is going to add.

Critical literature reviews helps to write critically. To write once own analysis of the subject, one will need to do careful critical reading of sources and to use them critically to make once own argument. Since the writing the rest of the research depends on reflections from what we have read, we must read critically. Critically written paper must have a balanced presentation of reasons why the conclusions of reviewed papers may be accepted or may need to be treated with caution. This is only possible through critical literature review.

Literature survey in process plant design, Part Two

2011-10-30T10:38:00.002-07:00

Problem statement: This section develops the main motivation for the study explaining real life problems to be dealt with. It is also called the rationale. In stating the problem it is best to specifically describe what the project intends to solve. For example, the possible real life problems may be shortage or even absence of the product in the local market, or to reduce the foreign import or to introduce a new and innovative product. The problem statement should specifically mention these reasons.

The justifications of the project, reasons for studying the problem, should also be included in this section. For instance, the fact that Brewery industries in XXX region mainly import malt while it was possible to produce the barely in highlands of the region could justify the malt production project.

This part is best written if specific numbers are mentioned. For instance, if reduction in foreign import is the main problem, the average import in 3-5 years and its implications should be mentioned. This will transform the problem statement part to evidence based argument than a simple general problem.

Objectives: This is the most crucial part of the project. It is the first seen by project evaluators hence leading to many critical questions. In writing the objective part the best format is to divide them into general objective and specific objectives and write at least three objectives in each category.

The general objective is derived from the statement of the problem. It restates how this project solves the problems and the overall uses thereof. For instance, for plant design project, the general objectives could be to satisfy local demand, reduce foreign import and save foreign currency, introducing new product that has market potential, create jobs and contribute to economy etc. Please note that writing bulleted one line statements as objectives is the worst way to describe them. So always write an elaborated objectives to make it clear to even the project evaluator who has little knowledge about your objectives.

The specific objective should state what specific tasks are planned in the study. For instance, the literature survey leads to identification of the state of the art in the production and review of current researches related to the topic. These results are one specific objective.

Another specific objective could be derived from the mass balance, energy balance and sizing chapters. This could be generalized as one specific objective i.e. to determine the exact size of the plant that can balance supply and demand or at least reduce the shortage.

The market and demand study is another source of specific objectives. The outcome of this study is to determine the demand of the product and the selling price that affect the financial success of the plant. This could be generalized as one specific objective.

Financial and economic analysis gives a specific objective to determine the financial feasibility of the process plant. The outcome of the environmental impact analysis section is summarized as one specific objective.

Methodology

The methodology of a project is details the principles, procedures or rules to be used. Plant design procedures are usually clear. It starts with literature survey, market survey, design calculations, may include laboratory experiments and ends with financial analysis and environmental impact analysis. These processes should be elaborated in the project methodology section.

Market study in process plant design

2011-10-30T10:38:00.001-07:00

Market study is the crucial part of the literature survey as it later determines the proper size of the plant and the selling price of the product. It contains present demand and supply, pricing and distribution and projected demand. The later could be made based on the past and current price trends. Also, it can be estimated from expected future scenarios (e.g economic growth, growth or decline of a sector etc). If figures are available, the average growth percent or the expected growth rate could be used. The estimate should be conservative. Always present a table showing the 3-5 years of annual production or import of the product.

Contents of Market study

Present demand and supply
Projected demand
Pricing and distribution
Production program

Example

Gypsum powder production plant

The present demand is derived using the available data on consumption of gypsum powered.

Table 1: Demand for Gypsum Powder

Year	Demand for Gypsum Powder (ton)
2002	66000
2003	68998
2004	56987
2005	701995
2006	74,545
2007	78,272

The consumption of gypsum powder is set at 82, 186 tons, in the year 2008.

Projected Demand

Assuming a 7% annual increment in demand for gypsum powder, a 10 ten demand projection is made as shown in Table

Year	Quantity (ton)
2009	87,939
2010	94,094
2011	100,681
2012	107,729
2013	115,270
2014	123,338
2015	131,972
2016	141,210
2017	151,095
2018	161,671
2019	172,988
2020	185,098

Pricing and Distribution

Currently, a kg of gypsum powers sales about $1500/ton. Allotting attractive margin for the distributors, the factory selling price is set at $ 1000/ton.

Plant Capacity

The envisaged plant produces 50000 tons of gypsum powder per year. The amount can be doubled or even triples without additional machinery by increasing the number of shifts, if this warrants the market demand.

Production Program

The program is scheduled based on the consideration that the envisaged plant will work 275 days in a year in 1 shift, where the remaining days will be holidays and for maintenance. During the first year of operation the plant will operate at 70 percent capacity and then it grows to 80 and 90 percent in the 2^nd and 3^rd years, respectively. The capacity will grow to 100 percent starting from the 4^rd year. This consideration is developed based on the assumption that market and logistics barriers would take place for the first two years of operation.

Literature survey in process plant design (Part One)

2011-10-30T10:38:00.000-07:00

The literature survey is best written if it is designed to contain the at least the following information; history and background, problem statement, methodology and objectives.

History and background: It reviews previous literature on related topics of the main research idea. Note that you should write only relevant information. Don´t fall in the trap of stating every trivial but non important texts just because you like them or want to increase your thesis volume.

For a plant design project, the best contents are short description of the process, chemical formula, chemical and physical properties, application and uses and source of raw materials.

Example

Below is a typical Literature survey contents in plant design project

Literature survey

● History and backgrounds

● Short process description

● Demand study

1. Current and future prices

2. Prices and price distributions

● Objectives

● Methodology