DMCplus控制器可以通過多種方式改善過程單元的操作和利潤率。在多數情況下，增加利潤的最好方式就是提高單位產量。對很多單元而言，通常將進料增加到系統接近激活到一些下游約束變量。

由于流程的多變量特性，可通過操作其它幾個變量消除該約束，但任一其它變量的改變都會激活其它一些約束。

例如，在流化床催化裂化裝置中（FCCU），將進料增加直到濕氣壓縮機達到它的速度上限。增加吸氣壓力設定值可以緩解速度限制，并允許更多的進料被引入，但吸氣壓力增大過多會激活再生催化劑滑閥壓差下限。

這一限制可通過增加再生器壓力設定值解除，但再生器壓力設定值的增加會激活鼓風機速度上限，故也不能增加過多。

對過程進一步復雜化分析得到的事實是，進料、吸氣壓力以及再生器壓力都會影響壓縮機速度、再生催化劑滑閥壓差和風機速度。

如上述例子所示，這是一個高度多變量過程。最佳操作點可能在壓縮機轉速、再生催化劑滑閥壓差和風機轉速都在極限內的最大產量處。

在化學反應單元中，提高利潤的最佳辦法是提高產率。大多數過程單元都是高度多變量的。加氫裂化裝置有幾個串聯催化劑床層，每一床層入口都有急冷流股流入。通常情況下，每一床層都有一進口溫度控制器控制急冷流股。為防止反應失控，每一催化劑床層受總床層溫升（溫度增量）約束。

為了增加產量需要更嚴格地對待關鍵指標，這可能意味著需要將其中幾個催化床層運行在上部床層溫升限或床層驟冷閥上限。

由于上游床層出口溫度將對下游床層驟冷需求產生影響，有必要考慮過程多變量性質以獲得最好收益。

若一單元中的某個產品相較于其它產品有較高的價值，通常可通過最大化回收該產品獲得利潤最大化。例如，天然氣液態工廠（NGL）中，它有超過150＃的蒸汽（蒸汽是免費的），脫乙烷塔從丙烷（如液化石油氣出售）中分離乙烷（燃料）。

由于蒸汽是免費的，并且丙烷價值比乙烷高得多，運行該塔利潤最高的方式是最大限度地從乙烷中回收丙烷（順帶在產品規范允許的范圍內于丙烷產品中留下盡可能多的乙烷）。

在另一些情況下，利潤最大化通過公用工程消耗最小化得到。例如，一個分級精餾生產苯、甲苯和二甲苯的BTX工廠。相較于產品價值，在此工廠中蒸汽成本更為顯著。

在這種情況下，將所有產品控制在產品規格所允許的最大雜質含量以節約能源是非常有必要的。這將節省可觀的蒸汽消耗量。由DMCplus控制器帶來的價值是通過努力監測過程干擾，推動產品卡邊規范，主動采取動作使干擾在影響過程前得到修正。

在一些經常受到相當大且頻繁干擾的單元中，穩定單元操作基礎將DMCplus控制器嚴格限定。經濟效益可以體現在下游控制器中。例如，加氫裂化裝置中分離C4（塔頂）和C5（塔釜）的Pre-Frac塔。氣態塔頂產物被送入氣體廠，塔頂儲液器液位由操作員控制。

單元頻繁進料組成變化將引起反應器床層平均溫度（WABT，重要指標）變化，這將會大大影響Pre-frac塔，自然也會影響天然氣廠。

該塔委托運行的DMCplus控制器可以穩定運行。因為穩定了Pre-frac塔天然氣廠進料，減少了天然氣塔的能源消耗，天然氣廠將獲得經濟效益。

一個典型的DMCplus應用程序將依據部分（或全部）上述列出的方式使利潤最大化。DMCplus控制器可根據其內置的線性程序辨識最佳操作點（自動辨識是最大產量還是最小公用工程消耗）。

事實上，由于產品價值和原材料及公用工程成本的變化，最佳操作點可能從產量最大化變化到處理量最大化。例如，催化裂化裝置（FCCU）在夏天可以運行最大化以生產更多汽油，然而在冬天則使燃油處理量最大化。DMCplus控制器的優點在于無需修改控制器以適應過程經濟情況變化。

附原文：

A DMCplus controller can improve operation or profitability of a process unit in a variety of ways. In most cases, the best way to increase profit is to?increase unit throughput. In many units, feed is increased until some downstream constraint becomes active.

Due to the multivariable nature of the process, several other handles exist that could relieve that constraint, but each of them will cause some other constraint(s) to become active.

For example, on a Fluid Catalytic Cracking Unit (FCCU), feed is increased until the Wet Gas Compressor is at its upper speed limit. Increasing the suction pressure setpoint will relieve the speed limit and allow more feed to be introduced, but the suction pressure can only be increased to the point that the Regenerated Catalyst Slide Valve differential pressure reaches its lower limit.

This limit can be relieved by increasing the Regenerator pressure setpoint, but it can only be increased to the point where the Air Blower reaches its upper speed limit.

Further complicating the picture is the fact that feed, suction pressure, and Regenerator pressure all affect the Compressor speed, the Regenerated Catalyst Slide Valve differential pressure,and the Air Blower speed.

As this example demonstrates, the process is highly multivariable. The best operating point might have theCompressor speed, the Regenerated Catalyst Slide Valve differential pressure,and the Air Blower speed all at their limits in order to truly maximize throughput.

In units that contain a chemical reaction, the best way to improve profit can be by?improving yield. In most process units, once again the problem is a highly multivariable one. A Hydrocracker has several catalyst beds in series, each with a quench flow to the inlet of the bed. Normally, each bed has an inlet temperature controller manipulating the quench flow. Each catalyst bed is subject to a total bed temperature rise(delta temperature) constraint, to prevent a runaway reaction.

To increase yield will require increasing severity, which could mean running several of the catalyst beds at either the upper bed delta temperature limit, or the upper limit of the quench valve for that bed.

Since upstream bed outlet temperatures will affect downstream bed quench requirements, it is essential to consider the multivariable nature of the process to obtain the best yield.

In units where one of the products has a very high value relative to the other products, profit can often be maximized by?maximizing product recovery. For example, in a Natural GasLiquids (NGL) plant which has an excess of 150# steam (steam is free), the Deethanizer is separating ethane (fuel value) from propane (sold as LPG).

Since steam is free, and since the propane value is considerably higher than ethane, the most profitable way to run the tower is to maximize propane recovery from the ethane (and incidentally, leave the maximum amount of ethane in the propane that products pecifications allow). The limit to recovery in this case is normally either atower flooding constraint or a condenser constraint.

In still other cases, the maximum profitis observed by?minimizing utility consumption.For example, a fractionation train in a BTX Plantproduces benzene, toluene, and xylene. The cost of steam in this plant is significant when compared to the relative product values.

In this case, it is worthwhile to save energy and control all products at the maximum impurity allowed by products pecifications. This produces considerable savings in steam consumption. The value added by the DMCplus controller is in diligently monitoring the process for disturbances, which would drive the products off specification; and making proactive moves to correct for incoming disturbances before they affect the process.

In some units that are subject to frequent and sizable disturbances, it may be that a DMCplus controller is justified strictly on the basis of?stabilizing unit operation.The economic benefits can show up in downstream controllers. For example, a Pre-Frac Tower in a Hydrocracker Unit separates C4's (overhead) from C5's(bottoms). The overhead product flow is a vapor that goes to a gas plant, and the overhead accumulator level control is performed by the operator.

Frequent feed composition changes to the unit cause changes in the reactor Weighted Average Bed Temperature (WABT, ameasure of severity), which dramatically affects this Pre-frac Tower, and consequently, the gas plant.

A DMCplus controller commissioned on this tower can stabilize the operation. The economic benefits are seen in thegas plant itself, since stabilizing the Pre-frac tower steadied out the gasplant feed, resulting in less energy consumption by the gas plant towers.

A typical DMCplus application will maximize profit in several (or all) of the ways listed above. The DMCplus controller, with its built-in linear program, can identify the optimum operating point whether that point is at maximum throughput or at minimumutilities consumption.

Indeed, as product values and costs of raw materials and utilities change, the optimum operating point can change from maximizing yield to maximizing throughput.For example, an FCCU can run at maximum severity in the summer to make gasoline and maximum throughput in the winter to make fuel oil. The advantage of a DMCplus controller is that it can account for changes in economic conditions and implement these changes on the process without modifying the controller.

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