Application of Pinch Technology and Analysis

Application of gazump Technology and analytic thinkingINTRODUCTIONThe term speck Technology was introduced by Linnhoff and Vredeveld to represent a new set of thermodynamically base rules that guarantee optimum energy requirements in design of heat trader networks. The application of Pinch technology to study industrial surgery is called Pinch Analysis.Applying first and second Laws of thermodynamics is requirement in Pinch Analysis method. The first law of thermodynamics enables us to use the energy equations in order to calculate the enthalpy change in the rain bucketss passing through heat exchangers and the second law decides the direction of heat carry because according to second law heat may only flow in the direction from het up up to cold regions but there conditions in heat transfer in heat exchanger the likes of1) No temperature crossover should be done since in a heat exchanger, a calefactive menstruation cant be cool down below the cold spud inlet temperatur e nor the cold drift can be heated up above the heatable stream temperature.2) In reality the sulphurous stream can be cooled down to a temperature defined by the temperature woo of the heat exchanger. The temperature approach is the minimum allowable temperature difference (DTmin) in the stream temperature profiles. The temperature level at which DTmin is observed in the process is referred to as twirp point.Pinch AnalysisThere be 8 steps in pinch analysis which areSteps of Pinch AnalysisIdentification of the glowing, Cold and Utility Streams in the runThermal Data Extraction for Process Utility StreamsSelection of Initial DTmin evaluateConstruction of abstruse plications and Grand Composite CurveEstimation of lower limit Energy embody scarsEstimation of Heat exchanger Network ( HEN ) Capital Cost TargetsEstimation of Optimum DTmin Value by Energy-Capital Trade falseDesign of Heat Exchanger Network1. Identification of the Hot, Cold and Utility Streams in the Proce ss* Hot Streams Hot streams that are required to be cooled down.* Cold Streams Cold streams that are required to be heated up.* Utility Streams are utilise to heat or cool process streams, when heat exchange mingled with process streams is non practical or economic.2. Thermal Data Extraction for Process Utility StreamsFor separately bouncy, cold and advantage stream identified, the following thermal data is extracted* Supply temperature (TS oC) the temperature at which the stream is available.* Target temperature (TT oC) the temperature the stream must be taken to.* Heat cognitive content flow rate (CP kW/ oC) the produce of flow rate (m) in kg/sec and specific heat (Cp kJ/kg 0C).CP = m x Cp* henry Change (dH) associated with a stream passing through the exchanger is given by the introductory Law of ThermodynamicsFirst Law energy equation d H = Q WIn a heat exchanger, no mechanical work is being performedW = 0 (zero)The above equation simplifies to d H = Q, where Q re presents the heat come forth or demand associated with the stream. It is given by the relationship Q= CP x (TS TT).Enthalpy Change, dH = CP x (TS TT)3. Selection of Initial DTmin pass judgmentAs discussed before and according to second law of thermodynamics no temperature crossover can be done. Thus the temperature of the hot and cold streams at any point in the exchanger must always have a minimum temperature difference (DTmin).In mathematical terms, at any point in the exchangerHot stream Temp. ( TH ) ( TC ) Cold stream Temp. = DTminFor a given value of Q, if smaller values of DTmin are chosen, the commonwealth requirements rise. If a higher value of DTmin is selected the heat exchange between the exchangers testament falling off and the use of utilities will increase. Thus, the selection of DTmin value has an imprtants and strong implications for both great(p) and energy apostrophizes.This table shows a typical DTmin of some industrial processesNoindustrial SectorExper ience DTmin Values1Oil Refining20-40C2Petrochemical10-20C3Chemical10-20C4Low Temperature Processes3-5C4. Construction of Composite Curves and Grand Composite Curve* COMPOSITE CURVES Composite frizzles consist of temperature (T) enthalpy (H) profiles of heat availability in the process (the hot building complex curve) and heat demands in the process (the cold conglomerate curve) together in a graphical representation.To realize the composite plant curve, a stream with a constant heat capacity (CP) is represented on a T H diagram by a straight annotation running from stream supply temperature to stream target temperature. When there are a public figure of hot and cold streams, the pee-peeion of hot and cold composite curves simply involves the addition of the enthalpy changes of the streams in the respective temperature intervals.For heat exchange to occur, the hot stream cooling curve must lie above the cold stream-thaw curve. This point of minimum temperature difference rep resents a bottleneck in heat recovery and is commonly referred to as the Pinch which is DTmin. Increasing the DTmin value results in shifting the curves horizontally apart resulting in lower process to process heat exchange and higher expediency requirements.In summary, the composite curves provide boilersuit energy targets but do not clearly indicate how untold energy must be supplied by different utility levels. The utility mix is determined by the Grand Composite Curve.GRAND COMPOSITE CURVE (GCC)In selecting utilities to be used, determining utility temperatures, and deciding on utility requirements the Composite curve doesnt provide so much information, thats why Grand Composite Curve (GCC) is used. The GCC (Figure 3) shows the variation of heat supply and demand within the process.Using this diagramthe fountain canfind which utilities are to be used. The aim is to maximize the use of the cheaper utility levels and minimize the use of the expensive utility levels. Low-pressur e steam and cooling water are preferred instead of high-pressure steam and refrigeration, respectively.To construct GCC the information required comes directly from the Problem Table Algorithm. The method involves shifting (along the temperature Y axis) of the hot composite curve down by DTmin and that of cold composite curve up by DTmin. The vertical axis on the shifted composite curves shows processinterval temperature. In other words, the curves are shifted by subtracting part of the allowable temperature approach from the hot stream temperatures and adding the remaining part of the allowable temperature approach to the cold stream temperatures. The result is a scale based upon process temperature having an allowance for temperature approach (DTmin). The Grand Composite Curve is then constructed from the enthalpy (horizontal) differences between the shifted composite curves at different temperatures. On the GCC, the horizontal distance separating the curve from the vertical axi s at the roundabout of the temperature scale shows the overall hot utility consumption of the process.The utility can be divided into some temperatures. The GCC indicates that we can supply the hot utility over two temperature levels TH1 (HP steam) and TH2 (LP steam). Recall that, when placing utilities in the GCC, intervals, and not real(a) utility temperatures, should be used. The total minimum hot utility requirement remains the same QHmin = H1 (HP steam) + H2 (LP steam). Similarly, QCmin = C1 (Refrigerant) +C2 (CW). The points TH2 and TC2 where the H2 and C2 levels color the grand composite curve are called the Utility Pinches. The shaded green pockets represent the process-to-process heat exchange.5. Estimation of Minimum Energy Cost TargetsOnce the DTmin is chosen, minimum hot and cold utility requirements can be evaluated from the composite curves.If the unit cost of each utility is known, the total energy cost can be reckon using the energy equation given below.6. Estim ation of Heat Exchanger Network (HEN) Capital Cost TargetsThe corking cost of a heat exchanger network is dependent upon three factors1. The human body of exchangers.2. The overall network area.3. The distribution of area between the exchangers.* AREA TARGETINGTo calculate the HEN minimum total area Amin ,divide the composite curve into a set of adjoining enthalpy intervals such that within each interval, the hot and cold composite curves do not change slope. The total area of the HEN (Amin) is given by the formula below, where i denotes the ith enthalpy and interval j denotes the jth stream and dTLM denotes LMTD in the ith interval.NUMBER OF UNITS TARGETINGFor the minimum number of heat exchanger units (Nmin) required for MER (minimum energy requirement or maximum energy recovery). The minimum number of units (NminMER) is the sum of the targets evaluated both above and below the pinch separately.NminMER=Nh+Nc+Nu-1AP +Nh+Nc+Nu-1BPWhere Nh = identification number of hot streamsNc= Number of cold streamsNu = Number of utility streamsAP / BP Above / Below PinchHEN TOTAL CAPITAL COST TARGETINGHEN capital cost (CHEN) is the capital cost is annualized using an annualization factor that takes into account interest payments on borrowed capital. The equation used for calculating the total capital cost and exchanger cost law is given below.C($) HEN=Nmina+b(Amin/Nmin)cAP +Nmina+b(Amin/Nmin)cBPWhere a, b, and c are constants in exchanger cost lawFor the Exchanger Cost equivalence shown above, typical values for a carbon steel shell and tube exchanger would be a = 16,000, b = 3,200, and c = 0.7.7. Estimation of Optimum DTmin Value by Energy-Capital Trade OffTo select an optimum DTmin value, plot the total annual cost which is the sum of total annual energy and capital cost versus values of DTmin.After plotting three important key features can be concluede1. If DTmin increases, the energy cost will increase but capital costs will decrease.2. If DTmin decreases,t he ener gy costs will decrease but capital costs will increase.3. Theoptimum DTmin is where the total annual cost of energy and capital costs is minimized.8. Design of Heat Exchanger NetworkIn designing the heat exchanger network it is essential to know which hot stream match which cold stream. Every match brings one stream to it target temperature. As mentioned before the pinch point divides the network into two separate regions, and each region is intentional separeatley.When the heat recovery is maximized the remaining thermal needs must be supplied by the utilities.The graphical method of representing flow streams and heat recovery matches is called a grid diagram .All the cold (blue lines) and hot (red line) streams are represented by horizontal lines. The entrance and exit temperatures are shown at either end. The vertical line in the middle represents the pinch temperature. The circles represent heat exchangers. Unconnected circles represent exchangers using utility heating and cool ing.To design the network and construct the grid diagram we use the CP Inequality Rule which states that the heat capacity flow-rate (CP) of the stream leaving the pinch needs to be greater than the CP of stream approaching the pinch, or CPout CPinSo above the pinch CPhot CPcoldAnd Below the pinch CPhot CPcoldAfter making all the possible matches above and beneath the pinch separately, the two designs are then brought together and usually refined to further minimize the capital cost. After the network has been designed according to the pinch rules, it can be further subjected to energy optimization.